flash kick is always air-blockable, even if done as deep as possible.
low fierce can be done VERY deep on certain characters and still win clean. It’s kinda weird, and is one of the more frustrating things about fighting Guile. You jump early over a sonic boom for what should be a guaranteed blocked jump in, and Guile just low fierces you really deep at the last second.
walk back and low forward
Walk back and throw out a meaty low forward for anti air, then control is back in your hands whether they blocked it or not. This is really important to know, particularly for characters whose jump ins Guile can’t stop without RC sonic boom. Especially handy for low jumps also. You can also link a level 3 sonic hurricane afterwards since you give yourself enough time to charge.
super jump roundhouse
This is Guile’s anti-air from half-screen to 3/4ths distance away. Throw a jab sonic boom, and if they jump straight over it just super jump roundhouse them on reaction. Will beat pretty much everything AND knock them back onto the sonic boom you just threw. Also works if they were about fullscreen trying to safely jump over a sonic boom.
level 2 kick super
This is one of the best defensive supers in the game. There’s almost no risk to throwing it out randomly since it’s nearly impossible to counter even if you think you know it’s coming. Works well in a pinch as anti-air, since the first hit has a gigantic hitbox that seems to snag anything in Guile’s general vicinity. Juggle the rh flashkick after for very decent damage, and control is in Guile’s hands.
level 2 flashkick super
This is kinda fun, but I wouldn’t recommend it in an important match. Level 2 flashkick super as anti-air, super cancel to a jab sonic boom to juggle, then cross up with super jump short. It’s actually really hard to block.