Clichy is offensively better (as in moving forward with the ball himself), quicker and better dribbler, offensive wingback, while Sagna is conservative and traditional fullback. But Clichy is too erratic offensively, too impulsive and not much in controll of what he is doing (Gibbs is smoother and more refined then him in this regard, more involved in linking with others), has great blitz runs but which have no end products (if he gets past them, he is impulsive with his runs, he generally runs too much into players and forced to pass along). Can do more individually, but when he crosses, which isnt so often be, he generally doesnt do much at all with them, he hits them very badly, like he doesnt have control at all.
Sagna is more of 2nd wave running off the ball and finding space off the shoulder of ze winger, limited offensively skill wise, but more tactical using that space and crosses decently enough, bit mediocre crosses, but fullfills this task dutifully and well enough, more involved working down his wing with others (seems more offensively willing lately), and hitting in crosses to finish off moves, in general find them to be better then Clichy's, who really, when he gets away a few, can barely get it close to any Arse player, its like a quota of 2-3 good crosses a season.