XCOM Class Analysis: Support
The Support is here to support your other units. They contribute little directly -Rifles have the worst damage output, and their skills lean away from improving their damage output- but are by far the best class for carting around a Medikit and in many ways are probably your best Arc Thrower users.
Once per mission, toss a grenade that provides +20 Defense to all units in the smoke until the start of your next turn.
This is not a promising start.
Okay, let's be more specific than that: Smoke Grenade broadly fits the idea that the Support is here to, well, support the other troops, but it's a weak effect you get to use once in a mission, so it's not particularly defining. It can also be compared unfavorably to the Heavy's basic skill -which I've already ragged on- of Fire Rocket, in that if you launch a rocket at some Aliens in Cover, you've added 20 or 40 accuracy for all your troops until the enemy's turn rolls around while also getting in 6 damage to whatever survived, where Smoke Grenade... subtracts 20 accuracy from enemy attempts to shoot you for one turn and... that's it. I mean, you can at least move before tossing a Smoke Grenade, but I have difficulty feeling like that puts it in league with Fire Rocket. The fact that the Support retains Pistol access is relevant, too, but... Smoke Grenade is just an underwhelming ability, and you'll never be confident it actually helped with anything.
Smoke was an actual mechanic in the original XCOM, too, and it was actually very, very useful, breaking line of sight and contributing Stun damage on units in the area. This was an incredible support tool all-around.
Support Smoke Grenades... not so much.
Sprinter OR Covering Fire
+3 to move OR reaction shots will trigger on enemy attacks. (In Enemy Within: the reaction shot occurs before the enemy attacks, not after)
Take Sprinter. Movement is huge, and +3 movement can easily be the difference between getting to someone who needs a Medikit right now vs having your Support unable to do anything before they die. It's always going to be good no matter what you're doing.
Covering Fire is garbage in Enemy Within and was even more garbage in the original game. Literally the only reason to consider it is if you intend to take Sentinel once you're max level, and frankly if you're considering that what you should be doing is dumping the Support for another Heavy and just take Bullet Swarm. Reaction fire is operating at an Aim penalty -one the Support can't remove!- and the biggest "benefit" of Covering Fire is letting you Overwatch even when there's Aliens in the area in the expectation that they won't bypass the Overwatch by shooting you... but in that scenario, why didn't you just shoot them on your turn? It's not until you have Sentinel that this makes any sense, but seriously, if your goal is to have a unit that can shoot twice in one turn, take a Heavy and grab Bullet Swarm. Bullet Swarm is even at the same rank as Covering Fire!
Field Medic OR Smoke & Mirrors
Medikits can be used 3 times per mission instead of once OR Smoke Grenades can be used twice per mission instead of once. (In Enemy Within: Smoke Grenades can be used three times per mission instead of once)
Basically the only reason to take Smoke & Mirrors is if you want your Support able to contribute without having to carry a Medikit.
I'm not sure why you're using a Support if you don't intend to have them carry a Medikit. An Assault is basically 100% better at pure combat, even considering Sprinter being strictly unique and a very good skill -Run & Gun provides equivalent functionality when it counts.
Revive OR Rifle Suppression
Can use a Medikit to revive a downed soldier at 33% health instead of simply stabilizing them OR spends two ammo to "suppress" a target.
Revive is kind of niche, albeit good when it crops up, while Rifle Suppression is the Heavy's Suppression skill with a very slightly different name for some reason. This runs into the problem that Suppression is, at base, a really godawful tool, and is only really worth using if you've got Danger Zone and Mayhem -things the Support entirely lacks. I'm not actually sure how Sentinel and Covering Fire interact with Suppression -I'd hope they treat Suppression reaction fire like regular reaction fire- but even if they benefit Suppression... we're still talking Bullet Swarm, but kind of awful, particularly since Suppression ends if the suppressor is injured for any reason at all. The fact that the Support has more Aim than the Heavy is more than offset by the penalty to accuracy you suffer for Reaction Fire.
So: take Revive.
(Update 10/9/2017: I'm almost completely certain Covering Fire doesn't affect Suppression. It certainly doesn't in Long War, and I doubt Long War deliberately made Suppression/Covering Fire worse)
Dense Smoke OR Combat Drugs
Smoke Grenades provide 20 more Defense and have a larger area of effect OR Smoke Grenades grant +20 Will, +10 crit chance, and +20 Aim to units inside their area. (But no longer provide Defense)
I default to Dense Smoke just because it's a pure upgrade to Smoke Grenade. Combat Drugs' bonuses are just too small/unreliable in trying to take advantage of, and it's easy to mistakenly throw a Smoke Grenade on the idea that it will provide some Defense, having forgotten that this particular Support is running Combat Drugs. Even if you default to Combat Drugs, you may make that mistake!
Maybe there's people who think Combat Drugs is hot stuff, but I honestly have no idea what Firaxis was thinking with it. Or with Dense Smoke, really.
Annoyingly, Combat Drugs doesn't actually mention that it does away with the Defense. I thought it was okay when I was under the impression that those bonuses were stacked onto 20 Defense, for one, but mostly it's kind of important to know. So why isn't the player being informed?
Provides a second inventory slot. (In Enemy Within: instead adds an additional charge on most consumable items)
In the original game, Deep Pockets was basically the only thing Supports had going for them outside of being Medikit masters, and it made them a favorite for carrying the Arc Thrower. With Enemy Within implementing Tactical Rigging, instead Deep Pockets is primarily notable for making the Support even more better-er with Medikits, since it now adds a charge to them. It also makes them your best Arc Thrower user overall, as it adds a charge to that, too. Note, however, these are the only two items where it's particularly notable -every other item that gets used up and thus is affected by Deep Pockets is either affected by the Heavy's Grenadier skill (Which adds damage in EW, remember?) or is Combat Stims, which for some bizarre reason doesn't get a charge from Deep Pockets. I don't really get why, given Combat Stims need all the help they can get to stay relevant.
Savior OR Sentinel
+4 health added when using Medikits OR fire twice on Reaction Fire.
Savior is of course the obvious end-point for a Medikit-focused Support.
Sentinel is... not actually terrible, for all that I indirectly ragged on it when talking about Covering Fire. Having Sentinel is actually decently useful for increasing your damage output when pods first enter your line of sight, and if you're playing the game at a high level of skill Medikit usage is a lot more niche, because high level play revolves around, as much as possible, preventing the AI from getting a turn at all. On the other hand, I don't like how it can create these awkward situations where your Support would theoretically ramp up its damage output by entering Overwatch rather than taking a shot -it's a bad design decision, in my opinion. This also comes back to the point that Supports aren't really designed to be your damage output units anyway. Sentinel and Covering Fire are the only skills that make a Support a better combatant, and "Overwatch specialist" isn't... really a valid niche.
I don't precisely feel that you should never take Sentinel, but I do feel that it's a poor dichotomy of choices, as the big draw of Supports is their Medikit specialization. A Support taking Sentinel brings you back to the question of "Well, why didn't you just use a Heavy or Assault?" The Medikit specialization is the only thing Supports have that really separates them from the pack in a positive way. So... I consider Savior to be very strongly favored over Sentinel for somewhat roundabout reasons.
The Support is an admirable idea with a flawed execution. Where the Heavy doesn't seem to know what it's supposed to be, the Support knows exactly what it's supposed to be.
... it's just not sure how to be that thing.
Sprinter and, arguably, Deep Pockets are the only skills on the Support that aren't clearly some form of attempt to keep them in a supporting role, but ultimately the Medikit-focused skills and, to a much lesser extent, the Smoke Grenade skills are the only skills that really push the support angle. The Smoke Grenade skills (Aside from Combat Drugs) are, themselves, a turn-ending attempt -notice, attempt- to reduce damage. In most situations just taking a shot and killing something would be a more reliable shot at doing so, particularly as you increasingly fight enemies that have attacks for ignoring Defense/accuracy entirely.
I'm genuinely a bit puzzled as to why the Support doesn't have any passive auras or the ability to, say, reload an ally's gun. The former bit particularly puzzles me since it doesn't seem to have been an engine limitation... more a conceptual limitation than anything else. It's also a bit wince-worthy to me how many supporting skills in the game are... actually on the other classes. Why do Snipers get Battle Scanner and Disabling Shot? Why do Heavies get Holo-Targeting? Why do Assaults get Flush? (Lightning Reflexes is technically a supporting skill, but it I completely understand)
I'm also not a fan of the fact that the Support lacks a unique weapon of their own. I would've loved to, say, see the capture tool be the Support side-arm. The only capacity in which being stuck with Rifles emphasizes a supporting role is that Rifles have inferior damage to the other main weapon types, and if Rifles were any more interesting than that, the game would run into the problem that Assaults get Rifles too.
For all that I ragged on the Heavy and Sniper's design decisions more, I actually feel it's the Support that is worst off, as the Heavy and Sniper's problems are centered around "Why would you make a choice other than the one that makes them meaningfully interesting?" The Support is... kind of a crappy class, with Medikit specialization being the main thing they bring to the table at all. If you're not taking advantage of that -whether because you didn't give the Support a Medikit or because you never actually used the thing- then they're basically worse than an Assault or, more debateably, a Heavy. It's a problem when an argument can be made that, of four classes clearly intended to be equal, good play should entirely avoid using one of them.
Next time, we cover the Mec.