The L-2000 is the most versatile of all three. It can emulate a precision, jazz, stingray, and 15 other tones--albeit not all 18 switching configurations are equally useful. Just make sure it has a 1.5" neck if you're digging a jazz neck.
Between the Fender Jazz and the JB-2, in my experience the JB-2 has better build quality. I've seen some strangely cut nuts on Fenders (including one that held the A string too loose so that it rattled). G&L's typically have more options available, since if you're ordering new from a dealer, you're pretty much ordering a custom instrument.
If you want a more traditional look and the namesake, get the Fender, but choose a good one.
Or better yet, buy a G&L JB. Best bass I've ever played, ever.