this is a matter of preference. the best setting would be the one which best suits your taste. just because you have a subwoofer, doesn't mean you'll automatically want to set your mains to small rather than large. it will depend on what you want to achieve.
for multi-channel surround-sound movies, THX standard guidelines recommend that the satellites (center, fronts, surrounds) should be crossed-over at 80Hz. this recommendation is based on their technical study which aims to give the best performance out of the playback system, mainly intended for movies. do note that this is just a suggestion, and the end-user is free to use whatever settings he deems fit.
for stereo music, there is no standard to speak of. there are audio purist who would insist on not using subwoofers and rely solely on 2-channel listening (i.e. L-R speakers only.) others would be more liberal, augmenting the L-R speakers with a subwoofer to either compensate for or boost the main speakers' bass extension (or lack thereof)