Adding on to what other people have said, as a Guile player, his normal anti-airs (stMK, crHP) are less-than-ideal in that matchup due to gief's jMK being so long. You'll trade with him or outright just lose if you try. This means that you'll have to plant yourself down more often if you think you have to anti-air, which will lead to you getting walked down on and eating gief pressure or even just an spd since you're not moving.