Disclaimer: The offline ranks are based on a recent AIM conversation with BAS, with a few of my own opinions on chars he didn’t mention. Those chars are denoted with an asterik (*)
Offline:
Rank
S: V-Akuma/V-Sakura
A: V-Karin/V-Sagat/V-Sodom/*A-Dhalshim/*V-Zangief
*“B+”: V-Ryu/V-Charlie/V-Vega
*B: A-Guy/V-Rolento/V-Chun Li/A-Gen
*C: Everyone else except
*D: Birdie/Juni (brunette, can’t remember if its juli or juni)
Online:
Rank
S: A-Dhalshim/AV-Zangief/ A-Chun
A: A-Ken/A-Gen/A-Blanka/A-Bison
C: Everyone else
Ok its easier for me to explain online since…well the tactics are easier and simpler, and I’m sure most of the people that read this forum mostly have to deal with online situations anyways
S Ranks
Dhalshim: Ok its bad enough that he can zone most anyone out at will and his normals are absurdly good, but with lag, you’ll end up jumping into his st. mks/hks even if the Sim player is randomly mashing. Also, jumping up attacks are really good online since going from one blocking stance to another blocking stance takes extra time, you’ll get hit by an “unblockable” jump attack! Plus Dhalshim can just mash cr. lk against a lot of characters with no chance for retaliation.
Things to counter him: Dhalshim is the only one of the S ranks who actually is hurt by lag. His b+mp and st. wp attacks are awesome anti-airs that unfortunately are hard to pull off with delay. Also, Gief, (once he gets in) has a lot easier time than offline since its hard to mash the st. wp to counter the Gief jump fierce (and variations) assault in time.
Zangief: Gief is a bitch character online. Any scrub can pick him up and win with two buttons: the hp button, and the 3p button (or if you’re on stick, actually pressing all 3 buttons). I should know since I play him 
J. hp/SPD mindgames are already bad enough, but when anti-airs are universally raped, it makes Gief’s game all that much better. To make it worse, Gief has a reliable practically lag-proof anti-air that beats everything except Chun/Bison stomp and Chun j. lk without worrying about timing…so mash that lariat!!!
Counters:
Dhalshim: even though his close game is raped by lag, he is still a viable anti-gief option with his far cr. mp/hp attacks beating out anything Gief does, as Gief’s cr. hp beats out of any of dhalshim’s other far normals.
Chun: stomp all day and do the followup crossup j. lk into whatever and you’re good to go, totally safe, idiot-proof plan. Add that to meaty st. hp->cr. rh stupidity and you have a viable online-only Gief counter. Oh yeah, and doing lightning legs randomly is good since the angle to attack her is bad for Gief.
A-Rank
A-Ken Ok, EVERYONE is wondering why I put A-Ken as top dog shoto online or even on the top list at all. Let me just say this is a personal grudge. Hadou Ken, who is a decent player in his own right, simply owned me 20 in a row with this character. Anybody who’s played me is prolly thinking, “Wow he must have dp’d every jumpin and had mad footsie skills or some broken VC!!!” No, he knew how to play the system for what it was. A-Ken has the best tool for online play: A uber jumpin. Ken’s air-Hk is for whatever reason, better than Akuma’s, and obviously better than Ryu’s. It travels faster and it seemingly lands faster than Akumas. Using it as a fast side switch is too good online where button/animation lag messes up blocking schemes. Offline its simpler to deal with it (Dhalshim b+mp owns air hks) but online its a bitch since the move, moves very fast and one’s own retaliation is not guaranteed. Alternatively, Ken can jab dp with impunity so if you are even a little bit late in trying to counter above scrubby air hk abuse, he will pop you. THis is not the same as trying in vain to react to a jump in with a dp before someone tries to bring that up, because doing preemptive dps is easy. With lag, A-ken becomes like a watered down version of ST’s O. Ken. Very slow fbs that can mess with jump moves, and a relatively unpunishable jab dp. If you’ve ever played DGV in ST, you knwo what it feels like, not fun at all but crazy effective
A-Gen
Gen is not that hard to play online. In fact he can be played a lot like Ken. Abuse the wall jump kick just like A-Ken would use air-hk because it will take advantage of lagged block input. Not to take anythign away from Johnny-Lemonhead (where is that kid anyway), but its not that hard to block that move, but I got hit by that move at least 5 times simply because the game hadn’t noticed that I had switched block directions. AND just like A-Ken, Gen’s dp move, waterfall kick, is hard to punish. Offline its already pretty safe, but online, just forget about it. Plus Gen can mash the first 3 hits for chip and still be safe.
GEN BONUS!!! Doing repeated jump up KKK style HPs on a downed Gief in the corner is almost inevitable guard break. It beats lariat clean! Plus it does fat guard damage. Mix in with random waterfall kicks and non V-Gief is done in the corner. hip hop horray!
A-Blanka
A3 Blanka is not CVS2 Blanka. He is not good…at all…offline. Cr. Fierce and all its variations suck, he doesn’t have Electric ball super, no RC electricity. Online, he is a GOD. He has the requisite awesome retard jumpins plus a fast jump. Blanka balls are a 2 frame (!) move. This is the fastest special move in the game and its only matched by Chun Li’/Sakura’s jabs. So with lag messing up movement, even the best player is going to get by at least one blanka ball during the vulnerable jump frames or just from the lag input. I’ve personally never had that much problem with Blanka players, but I’ve had plenty of people complain about how good he is in comparison to his “real” offline incarnation.
A-Bison
Bison is one of my favorite chars in A3, no lie. If A-Bison had X-Bison’s stomp followup I’d play him as one of my mains no lie. Bison is much like Blanka in that he has a funky fast jump and good priority on his jumpins (j. lk/mp/hp and jump up mk). Unlike Blanka he has awesome supers and good ground normals.
Bison’s game is simple: throw a slow fb and if the opponent jumps, meet them with a j. lk or jump up mk. If they stay grounded (and are far away) do a stomp. If close, walk forward and st. mk. Cancelling block strings into stomp is way too good since this move takes advantage of “lag block error”. You have to commit to the high block so early that I can just mash cr. mk->super just to fuck with you becuase you SOOOOO want to stop getting hit by the stomp, the annoyance factor is very high, that you block high early to compensate. Also, Bison, if he really wants to be gay about it, can just teleport away indefinitely due to the slower reaction times most characters have to deal with. He can also mix in jump back mps which is 2nd only to Dhalshim in “runaway jump move” range. I remember Smooth Operator back in the day used to do this and I got pissed just trying to chase him down, whereby I then immediatley co-opted this tactic for my own 
I can see that his rushdown game could be harder to deal with with lag though. Shit I couldnt even time a jumping rh online lol… Shit would come out when I hit the ground.