Frat Rush/Bid Process

Ive been in contact with a few rush chairmen and hear that most fraternities have summer events that are around frog camps and orientations. Is there a better camp/orientation time to attend when there is more events? Also have been reading all the "top houses stff", is it harder to get a bid at one of the "top" fraternities? Thanks to anyone who responds, didn't wanna pester the rush chairs with questions like these...