I have both. Initially I was more interested in the gargoyles because of their colors (all cresties seemed to be brown to me, regardless of the morph name). I find cresties to be more active and jumpier, so they can also be more entertaining. While I think a larger cage size is better, I'd put a gargoyle in a 12x12x18 cage sooner than I would a crestie because the gargs spend a lot of time just sitting. Now that I've found some more interesting colors (only 1 of my 5 adult cresties is brown), I'm enjoying the cresties as much as the gargs.
Aliza