Depends a lot. If they recover crouching it's 2A+G_B+G. If they recover standing 66B at i17 and 35 damage (45 at tip) tends to punish better than bullrush at i18 and 28, although BR knocks down. The average damage from a command throw mix-up also falls into the same region in terms of speed and damage, so it comes down to being an issue of preference.
66B: Most damage, fast, and usually the best way to finish an opponet if you know it's going to kill them.
Bullrush: KD on hit, forces CF & Ukemi game.
Throw: Command throws are great for attempting to punish for more than 66B, keep in mind that they can be broken so choose this wisely.
Crouch Throw: same as above.
3A+B: Best CF Punisher for asta. Yes, you do sacrifice damage for this type of punishment, however this will come very handy late in the CF game. Forces your opponet to respect your strategy and causes them to think twice to throw that move out again. Now this will punish some moves also. If that's the case, it will force a ukemi/CF game.
Typically, asta's will throw out the top 2 that i've mentioned. However, well-rounded asta's will utilize every means possible to throw fear into their opponets
For block punishing I prefer to punish -17 moves with 6K over 66B unless ...
1) 66B will kill (duh)
2) 6K will not reach due to push back (think Mitsu's RL B)
3) Against some moves with fluctuating negative frames (because 6K is easily punishable and 66B is not)
The reason is that, after 66B hits, you're only at +2 at a really awkward range. Not close enough for 4B pressure but not far enough for spacing either. I would also prefer bullrush punish over 66B as well ...
I don't use K/2K/6A to punish unless I know it'll kill.
There are some technical punishing situations that involve using PT to punish low-high strings but those are really hard.
I would be using 4B to punish a lot more if it at least forces crouch haha.
But, no seriously, if they're doing three or four moves ('spamming', as you say, as opposed to attacking stategically) and beating you, you should probably look at what you're doing wrong as opposed to what Ast can do.
But it'd help if you gave an attack pattern and explained why it gives you so much trouble. And...hopefully...not be talking about online.
You could check the wiki, information should mostly be there, but iirc...
i21, High, TC from frames 5-14, aGIs high and mid weapon based, non-thrust attacks 15-20, TJs starting at frame 15. It knocks down on counterhit is -2 on normal hit and is unsafe on block (-16). It's not a very good aGI since it starts so late (and sucks on NH), but at least it TCs nice and early. Because it TCs into a high aGI, it will JI high horizontals with multiple active hit frames with less precise timing.
umm, notation??? FotW > 22[K] is not a combo if that's what you're asking. It deals a lot of damage for opponent not teching the FotW knockdown. If opponent techs and blocks low you get nothing(other than the break in 11 block off 22[K]). Some claim the 22[K] can be teched on reaction, though it has not been my experience that it's true, at least for most people. If opponent techs and doesn't block low cause they aren't used to the set-up you can get nice stuff like AB > 1[A]B(B not hitting in all circumstances, but thats ok too since it's +12 on block).
If what I answered was not your question, please rephrase and I'll try again.