I have a 35" 5ver and two 34" ones. I dunno, the laws of physics state that 35" will give the B a tighter sound, but a lot of people on here will tell you that a $3000 34 will overcome that in some way. I sat in the Sadowsky shop and experienced this first hand, though I couldn't tell you how they do it. It's possible that string choice plays a big role.
But a lot of it depends on your feel, as well as what brands you already like. For instance, the name Music Man has popped up on this thread several times as an example of how to do it right. But honestly, I tried out a whole bunch of Music Man 5vers, and found none to have the holy grail of B strings. I bought a 35" scale Lākland instead, because it had a B string with some real zing in it; I don't want a B string that feels better than one on a cheapo bass, I want one that feels as close to an E string as possible, flab-wise.
Granted, I then turned around and bought a Fender 5ver, which is 34" scale. Again, some on here have mentioned that string selection can really affect things, and I definitely *do* buy that argument. I think I've found a string set that gives me a good B, but I'm always on the lookout for a better B.