Get the Yamaha. Yamaha pickups are absolutely great. The BB734A for a little more has the same pickups as their pro model and is one of the best bass values for the money out there - a lot of people argue it’s the actual top of the line.
The 434 is great too, but you get a lot of additional value in the 734A.
Plot twist: if the stock preamp in the Yamaha is as good as in older models, you can go with rounds and turn trebles down so much it sounds like flats.
I had TI Jazz flats on my BBG4, and while nothing beats the feeling of those, I recently went back to rounds because they offer more possibilities and sit better in a mix of instruments.
The factory combo of pickups & preamp is so well matched I don’t want to change anything in that bass.
I just wish those rounds were as silky smooth and soft like the TI flats.
I’ve not played the bb434 but I played the usa lb-100. I have no doubt that the Yamaha will be amazing. Choosing between the 2 choices for me comes down to number one, nut width. It doesn’t matter or even noticeable to mod but to me it’s the first thing I look for in a 4 string bass.
This is huge between these 2. The BB434 has the nut width is 1.57” and the LB-100 is almost a quarter inch wider at 1.75” the original with of the P-bass that’s even wider than the current champ, Musicman stingray at 1.687” my favorite.
Playing them side by side the 434 would feel faster and more nimble if that’s your thing. I like the more generous spacing of the 100 for sure.
Both basses would come home studio ready with kick a$$ tones even on flats.
I love my ASAT CLASSIC S. It’s pretty awesome especially with the G&L quirky electronics, lol.
I’m visiting my parents this weekend in a slightly larger town than where I live. I managed to find and play a Yamaha BB234. Nice instrument, but I didn’t love the narrowness of the neck at the nut. I’m sure that I could get used to it, but I think I’ll go with the G&L with its larger neck.