Mossimo Black, hands down. I love the simple sleek elegance of it, all the while still having some believably casual pieces. Merona's fine, but it sometimes screams "housewife", not to mention Knox Rose while usually alright tends to feel very "I'm a self-described country girl who actually lives ten minutes outside of the suburbs and wears cowboy boots and pink hunter camo strictly for aesthetic purposes." Aaaaaand Mossimo Red is fine. It has its ups and downs, probably the most stable collection following Mossimo Black.
Also, Xhiliration looks like someone's creepy aunt who was a colorblind tasteless party girl in the 70s donated all her clothes to Goodwill and no one would touch the stuff. Seriously, who is designing this shit?