I've had a JamMan Solo and an RC2, sold them both (and wish I hadn't) but I'm looking at another, and I'd go with the Boss, probably an RC3. The drum tracks are way better on the Boss, everything else is pretty similar, feature-wise.
I'm still using the Boss RC-20xl. Does just what I need.
However, have you considered something like the Line 6 M9, or the Zoom G3? Both work as loopers plus you get loads more functionality as well. For the money the Zoom is a steal, and there's usually loads of second hand M9s floating around the classifieds here.
Actually NTD has a good point too. I already have a G3 on my board but I'm considering getting another to use at home just for the looper, as it has all the features I'd want from a looper at the same price as an RC3.