Like many other things in life, it is all a question of trade-offs and what is most important to you. All things being equal, the longer the scale length, the more taught any given string will be at a given pitch (i.e. a 34" B will be under more tension when in tune than a 33" B, and a 35" under more tension than a 34").
The issue that really is key is -- what do YOU personally feel is "enough tension" that the string does not feel floppy and this is highly subjective and depends on many things including playing style (e.g. light finger-style work vs. heavy slapping). No B-string (not even a 33") should ever feel flabby and sound dead and/or diffuse if the instrument was properly made, set up and the strings are of high quality and fresh. However, even if all of that is properly done, someone with an extremely sensitive touch will feel a difference between scale lengths -- especially on a B-string. I certainly can.
Now I am just a 4-string guy and personally play only 34" scale basses, so I could not begin to tell someone where that line of "Wow this feels great, it's only a 33" scale?" turns to "This is okay, but I really wish the B was under more tension." But what I can say is before deciding something like that, understand yourself and what your goals for the instrument are...
1. Is the size of the instrument critical (i.e. do you have small hands, shoulder problems, travel a lot and want something compact and easy to carry on planes)?
2. Does your playing style tend towards a light right hand technique or are you dig in in a big way?
3. Do you like your strings to feel like they are under a lot of tension, or do you like a looser feel to them?
4. Do you record a lot / Tone? I am not going to touch this one personally because it can be a bit of a lightening rod, but there are top players in both camps. One camp is the longer the scale length, the better the sound -- especially on the B and E strings. The other camp while generally acknowledging that a longer scale length instrument might sound better in an absolute sense, feels that it is not significant enough and/or audible in the real world settings in which we play that it makes much of a difference. This said, I know at least two of our top players (who shall remain nameless) that have largely identical basses -- one they gig with and the other the take into the studio. You guessed it -- the 34" scale basses go to the studio and the 33's head out to gigs...trade-offs, gotta love 'em.
In the final analysis part of the art of building at this level is helping someone understand how each decision they make (and which scale length is a pretty big one) will effect the instrument that shows up on their doorstep a couple of years down the road. Couple that with the way Vinny, Joey and Vadym build them and you've got a very good shot at getting a killer instrument that perfectly meets your needs.