they act much the same, though i have heard the gargs are more scared of people or jumpy like. One thing they recommend you keep each garg by itself since they tend to bully eachother. Cresties you can have groups of them sometimes together with no problems but need to keep eye out for bullying. Personally i like cresties better but one day i want to get into gargs.
I have always been fascinated with gargoyles.I've heard when juvie gargoyles are housed together they tend to bite the tips of the tail of the other geckos.
I've never kept a crestie but I know plenty of people that do... honestly, you can't go wrong with either. From what I know, gargs are more tolerant of lower temps and humidity (not that that's any excuse to slack off on temps and humidity) and don't get along with other gargs while cresties are moderately social.
About temperament, I've heard that gargs are calmer than cresties and visa versa.
Personally, I prefer the looks of gargs; they've got such unique colors, and I love their fat little bellies.