I’ve found playing Vega primarily grounded to be very effective, except for the problem of having to generally be a turtle.
Before I go on, I’ll point this out: I’m primarily playing on CvS2:EO on the Xbox with a Controller S, using controls modified for KOF/CvS1 usability. (Jab=X, Strong=White, Fierce=Black, Short=A, Forward=Black, Roundhouse=B.)
A fully grounded Vega is virtually impossible, requiring a Roll-capable Groove and a ton of luck. (Oh, and an opponent that’s a complete rookie, such as an EOer barely converting to AC-ism.) So obviously I don’t play without some form of jumping. But I completely neglect airborne specials. (It’s really because of the S’s inferior D-pad, but my strats still work.)
The obvious key to even semi-consistant winning with Vega, ground OR air, is maintaining his claw. Do whatever it takes to regain the claw in case of its loss, ne? The mask is also important, but since you really don’t wanna get hit anyway, it’s not AS important.
For defense, I tend to play it classic style. I jump back and block. Unfortunately, turtling gets you screwed in the Guard Gauge, so it’s easy to see it, freak out, and go into a reckless offense which can get you really screwed over. If you know what you’re doing when you’re restoring your GG, go ahead and attack. But it’s probably better for less-experienced players to take the hit. If the opponent can’t follow up a Guard Crush with a Super Combo. Also, don’t try to counter a Shun Goku Satsu with a Rolling Crystal Flash. It’s just not gonna work. Just about any other strong close-range attack, however, should be dealt with with a block to RCF/Fierce. Air attacks should be blocked or countered with Scarlet Terror. But a correctly-timed jumping Roundhouse works wonders due to the unusually high priority on the attack.
As for offense, it’s mostly just countering Fierce/Roundhouse close-range attacks. If you’re against a long-range opponent, like a rookie Terry or Ryu, you can try a jump-in Roundhouse during a Hadouken or Power Wave or Kikouken or whatever. Just make sure the jump’s early enough to not get pounded by a Power Dunk or this website. Also, use Red Impact whenever you get a clear shot with Lv.3/MAX. For example, if your opponent’s gonna attack or jump, if you hit the button just as it happens, you’ve got him. Barcelona-brand Instant Lunch, steel flavor.
Also, you’ve got to deal with certain specific characters. The obvious one, all the way back from SFII, is Bison. Deal with the Psycho Crusher by blocking, following up with a ducking Fierce as he passes by. (Or if you feel REALLY lucky you can always Red Impact. Hits by the defender on an attack’s extension always counter that.) Deal with a Double Knee Press with a ducking block then ducking kick. Unless your opponent’s on EO, a Roundhouse should be safe. SHOULD. If he does a Super Combo, use a Triangle Jump or High Jump if you’ve got the room to jump at all. Both should clear it with proper distance. If you’ve got Lv.3/MAX, the GG, and the HP, it could be a good idea to block it in hopes of getting that Red Impact in and doing massive damage.
I know, a Vega without his air specials isn’t really much of a Vega, but it turns out to be very useful. Nice bit of surprise for the opponent that knows him. (And a typical Vega will pretty much work anyone where I play, since I’m the only real Vega user and I play grounded Vega.) If you can figure it out, it works very well.
How well? There’s this one guy that’s deemed the master of video games. (At least at this Gamecrazy in Duarte. He wins almost every tournament at almost every game.) I completely devastated one of his best teams (Ken/Ryu/Terry) with just my grounded Vega. Twice in a row. (Except the second time he still had about 500 HP left on his Terry when, on the sixth consecutive round of my using Vega, he got KO’d, so I made short work of him with Guile.)