Good Jazz Amp?

You are much better off asking on the Electric Bass side of the board. Do a search first off all. There is a TON of information on this site. And its very likely your question has been answered in several threads. There are a lot of great amps out there and you will need to give an idea of your price range, power requirements, groups you will be playing with. About 90% of my gigs are Jazz. On the rare occasion that I use a bass guitar I will bring out my Gallien Krueger MB112 combo.

 

Any clean accurate portable amp and cab will do.
Personally I'm digging the Genz Benz Streamliner 900 with either a single Bergantino HT112ER cab or, even better, the Berg HS210.
IMHO YMMV etc.