I feel the G&L has better tonal options. It's also lighter from my experience. My friend is a 'wick fanboy and would swear to the Thumb (I have played it and it is a wonderful bass) but the G&L blows it out of the water.
I was at Guitar Center this Saturday. For two and a half hours I sat there and played a 1981 L-2000. My god, it is the best thing I have ever played. I'd try another bass, but I'd feel like something was missing and just went back to it.