Well, most yuri tends to just be mindless, meaningless sex and fanservice (prime example being the h-manga Vanity Angel where both of the girls are staight but for some ridiculous reason they have sex and makeout regularly) but occasionally you get serious drama (Strawberry Panic, Kashimashi) and even action (Burst Angel, Kannazuki no Miko). Then there are shojo-ai stories that include light elements of yuri (Shinobuden, Oni-Gokko, To-love-ru).
Not saying that yaoi doesn't get just as raunchy for no reason but most yaoi seems to be tame in content and more about true romance (it's aimed at females so "sex, sex, and more sex" as a plot just won't cut it).
That being said I'm an 18 yr. old male so I'm going to have to go w/ the choice that involves the most naked women.
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