I wear the beach style...I have wide, flat feet, so they work best for me. Others with narrower feet have mentioned that the cayman are sized more normally (they come in full sizes, as opposed to the beach, which are combined sizes like 5-6, or 7-8, etc).
I've bought mine several places...Dick's Sporting Goods, Eastern Mountain Sports (EMS), Stide Rite (for my DD6).