XL is all around better, larger screen aside the other better parts are the battery, far less screen reflection, nicer buttons and that it's just more comfortable to hold.
I was freakin' the other day because my XL died in sleep mode, like within a day (turns out it was fine, just left wifi on by accident and didnt know street pass ate that much). I went ahead and rigged up a battery test on it, putting it through perpetual replay in Mario Kart with full sound and 3D on, and it lasted ~7 hours, pretty damned slick, that's higher than quoted even I think. I was kind of shocked that it kept on trucking that long. (settings: 3/5 brightness, power saving on, no WiFi)