Shuma should be using low RH (into FB) as air defense, and c.strong or c.fwd into FB, at mid-to-long range. In close, he should be doing dashing jabs into command throw (his s.jab is the fastest in the game), or the kick throw if you can get it. Kick throw = free launch (and super) against all characters.
Against the pixies, the dash jab into command throw is not really worth it. The most effective strategy is to proceed directly to your corner; do not pass go, do not collect $200. Once you are in your corner, you can play your air and ground defense game, and do things like jump and airblock an air attack at the last second, then land for a 50/50 throw attempt. Spidey and Wolvie can’t follow up their throws with anything in that situation, and if you get the throw, they should be dead. If Spidey tries to throw FBs at a distance, dash under them and c.fwd him.
Spidey’s is great when Power Gem is active (~40% life). Spidey also has no other use for his meter, so AC away. Jug should not really be wasting meter on ACs, as he needs them for supers. You can AC a cornered opponent, then do OTG c.short-Headcrush; if it kills them, then it’s worth the two levels.
As far as the others, Cap’s is also pretty good, and as mentioned, Hulk’s is as well. You can combo off of either of these (but it is not guaranteed). I don’t think I’ve even seen Shuma’s AC, as he needs meter for CD. Psylocke’s has pretty good priority, as far as that goes.
The characters with the worst ACs are BH (I believe Dark Thunder’s invincibility frames run out before the hit frames actually appear), Iron Man (pixies can duck under Repulsor Blast at point blank range, making it useless as anti pixie-rush), and Magneto (the 1-hit Shockwave is fairly easy to bait-and-block with a c.short, as it’s pretty slow). Of course, considering IM and Magneto have essentially infinite meter, that’s not so bad.
Runaway photons. Believe it or not, Anita has very little in the way of block damage (the super is not easy to land on someone intent on SJing repeatedly, especially someone with flight). Also, in general, never use Doom’s RH dive (it can’t be cancelled into flight, and is very vulnerable). Use the d+Short dive, chain to j.strong, then cancel to flight.