This thread is going to attempt to explain why it’s commonly said that Guile does well on Sentinel. Hopefully, this will get some people to offer help on this much misunderstood fight.
Anyway, these are Guile’s main weapons on Sentinel:
SJ. flash kick. This is the bulk of his anti-Sentinel repertoire. Why? Its priority is unmatchable AND it puts an upward moving projectile on the screen, which in short means that Sentinel can’t fly offensively on Guile safely. To be successful with this move you should learn how to pull it off on the fly (simplest method is to just superjump again with a short/RH) and when to do it (when Sentinel is above you, pretty much). This takes away a lot of Sentinel’s game.
Jump roundhouse. This move’s range and priority is just too much, and when used well, it can prove to be a major annoyance to Sentinel. What you want to do is use this move a lot when you get past frying pan range. Since it breaks super armor, Sentinel has to either block it or get hit. It’s not easy to combo after this. I don’t recommend trying, unless you know you are low enough to do it. But harass him with this move once you get in this range.
low short -> low forward (plus assist) -> low rh (1 hit) xx jab sonic boom. All blocked. When you get within range, jump roundhouse plus this blocked chain (especially if the assist is a good projectile assist like Sentinel) makes it very difficult for Sentinel to get away from you. Once it’s done, there is a fireball on the screen. True, Sentinel can clear it easy with low fierce xx fly/unfly, but that makes it very easy for your jump rh to hit him (and no, he can’t get a frying pan out in time).
There are other important moves of Guile’s (c.fierce and superjump meter charge) that help the fight, but these are the bulk of it.
General plan with Guile vs. Sentinel at start of match - jump towards him with jab -> jab -> roundhouse, and land and do the blocked chain ending in jab sonic boom. Watch out for AAA, and move in again with jump roundhouse. If you can keep Sentinel from getting aggressive, do so - remember that Sentinel is a good battery if you let him. You should watch out for AAA at all times (read, make sure you keep Sentinel blocking as much as possible) and look out for guard cancel possibilities (not many do this, but it can mess you up pretty good).
Guile’s use as an assist vs. Sentinel is also important enough that you should try to keep him alive. So, if you get a hit in and your health is languid at all, do a DHC combo to get your next character in. If you are good at doing his aircombo ending in super, Guile’s not a bad character at all to have in endgame, so don’t worry about this.
Keep in mind there are two things Sentinel can do which can end your fun: drones (especially roundhouse drones) can impede your lockdown plan; and Blackheart assist (keeps you from taking to the skies to turbocharge meter AND air flashkicking at will to keep Sentinel from flying). Guile has to take alternate plans against these which are not nearly as stupid effective as what I’ve outlined here.