I’ve owned the G&L JB Tribute with the ash body, and I currently have a Squier VM 77 jazz. Both are excellent basses and very comparable. I’d say the G&L has a slight edge over the Squier, but not by much.
Here’s a quick comparison of differences if it helps:
VM has a true jazz nut width, JB has the far better bridge IMO, fretwork on the VM is slightly better than the JB, the JB has a downsized P bass-ish body compares to the true jazz shape of the VM. Tuners are about the same. The weight of the VM and JB I had were very similar, not much difference at all.
I’d honestly go with whichever bass you like the looks of and can get a good deal on.
Here’s a quick comparison of differences if it helps:
VM has a true jazz nut width, JB has the far better bridge IMO, fretwork on the VM is slightly better than the JB, the JB has a downsized P bass-ish body compares to the true jazz shape of the VM. Tuners are about the same. The weight of the VM and JB I had were very similar, not much difference at all.
I’d honestly go with whichever bass you like the looks of and can get a good deal on.