Lets talk Size

Yeah, I know, I'm following the lead of electric wanna-be upright players. I'm sure all the experienced players out there have heard this question many times before, but what are the benefits and problems with different sized basses? There a p.o.s. upright laying around my school bandroom (when I'm done with clarinet I make my humble efforts) that I believe is a 3/4, and I can handle it decently well. Any responses would be appreciated.