I had a JC120 back when I was playing a lot of jazz in college. I played an Ibanez Artstar (if you can find an older one of these, before they went downmarket, THAT would be a great jazz guitar), and it sounded amazing with my archtop. It has a real spring reverb, and the stereo chorus and tremelo are really cool. Great amp for keyboards too, and it will have a nice clean tone for vocals.

Forget about overdrive sounds. You'll NEVER get this amp to clip naturally; it's solid state for one, so you wouldn't want to, and it has SO much headroom. I could get crisp, clean sounds on my archtop at ridiculous volumes - more than enough to blow away an entire big band in a big hall. It was always underwhelming when I played my Strats through it though. Made them sound way too trebly, like I was playing through a PA.

I like the Peavey Classic series. It matches with single coils nicely, and even though mine is huge and ways a ton, I'll pull it out for jazz gigs when I want a little more headroom. Although, if you hear live recordings of the guys like Wes, Kenny Burrell, etc, a lot of times they're pushing small tube amps into overdrive when they really get into their solos. So find a combo that sounds good to you; just because the Roland Jazz Chorus/Jazz Box combo has become the standard, that doesn't mean it's the only way.