The sound quality depends on what you put in front of the recorder. The mics will make a difference. Any preamp/AD will make as much of a difference as the microphones will. If you put a good A/D in front of the JB3 or PCM-M1, your results will be the same. If you can't afford a preamp/AD, (like the UA5 or AD-20), then you'll be better off getting a PCM-M1, it is better equiped to handle live audio recording.
What kind of microphones were you looking at? Any ideas on an external A/D? Most importantly, what is your budget like at the moment?
All things being equal, I think I would go with the JB3 these days, DAT appears to be on the way out with more reliable hard drive recorders coming onto the market. The Creative Nomad Jukebox 3 is the best example of small reliable portable hard disc recording at the moment. It will make conversions very easy - just plug in the USB or Firewire cable, and you can download a three hour show in around five minutes! If you go DAT, conversions will only be as fast as the length of the tape (barring high speed DDS drives, which are rare and sometimes difficult to set up).
I'm sure there will be other opinions posted soon, hope I've helped, and welcome to TS.com!!