Quitting is usually the best thing to do cuz Akuma is insanely strong and nobody should be using him. But if you’re a sucker for punishment, then there are some Ryu strats that can help:
The most dangerous mixup is the crossup Air Hadoken, cr Forward, Tatsu. The best way to block this is to hold back (which becomes forward once Akuma has crossed over), and then switch to back once the Hadoken is blocked. Sometimes the Hadoken hits after Akuma’s cr Forward, which makes it tough to block. But usually it doesn’t.
Instead of blocking, you can beat this crossup by doing the reverse Shoryuken motion (F,DF,D,DB Punch). Sometimes the Shoryu will go the wrong way, but it’s still to your benefit as the Akuma player may not be fast enough to punish the DP.
To beat Akuma’s neutral jump, Air Hadoken spam, a jumping High Air Tatsu works best from about 1/2 screen to 3/4 screen distance. If you’re too close, the air fireball will beat the air hurricane.
And if you’re throwing Hadokens vs his Air Hadokens, try to time your fireballs to go OVER his Air Hadokens, so that Akuma has to deal with it by jumping again or blocking. If you let your Hadokens hit his Air Hadokens, he has the recovery advantage and can hit you with a sweep or a Tatsu or something else.
If he Teleports a lot, neutral Fierce works pretty well, it will hit him even if he’s slightly behind you. The Teleport is only invincible during startup and recovery, but while it’s travelling it can be hit almost any attack that isn’t low and isn’t a fireball. If he Teleports just outside neutral Fierce range, you can still recover fast enough to not be punished. Or you can just jump away instead of dealing with it, but usually Akuma can hit you with a Roundhouse.
If you see a Raging Demon, get the hell out of there ASAP! Best bet is to jump away, just hold UF or UB and usually Akuma cannot hit you. Raging Demon is also vulnerable during recovery, but it’s not worth punishing it unless he’s out of throwing range.
I’m usually ok with playing vs Akuma in ranked, but nowadays there’s a group of dedicated Akuma players whose skills have improved recently (meaning they went from below average to average, but since they’re using Akuma who is overpowering, they are almost impossible to beat now). So I just ragequit cuz it’s not worth the aggravation. And even if you manage to beat them, sometimes they’ll just quit on you anways, so f*** that. Hopefully if enough people do it, they’ll get the message to stop using Akuma (not likely).