3/4. Bigger the bass, better the tone you will get for your money. It's the same reason a million dollar bass will never sound as good as a $5,000 cello, the proportions. In an orchestra the violin and cello have a brighter, better sounding tone. In order for the viola to have proper proportions it would have to have an endpin and he played like a small cello. One of the reasons an orchestra sounds good is because the violin and cello are bright, while the bass and viola are not. Look up the octobass, that's the size a bass would need to be to sound good, of corse the sound is so low on that instrument it's impossible to make a sound good to our ears. Long story short, play a 3/4. Or 1/2 if you really want to that much... When I first played my school but me on a tiny 1/4 or smaller or something and now I can play 3/4-7/8 but based on my genetics I probably will never be able to play a full. Listen closely to the instruments and if your ears are trained you will hear the difference of the two.