What's the best vocal looper to buy for live looping

[music@carlsonarts.com]

Hello everyone, I have just joined the email list, but I'm really  
exciting about using a looper in live performance.  I remember seeing  
Phil Keaggy (a guitarist) using one like, 20 years ago, and I was  
blown away.

This list is awesome!  It's going to help me realize a life-long dream  
I've had to "be the band."  I am a professionally trained and seasoned  
male vocalist, with a college degree in music, interested in getting a  
looper that works especially well for exclusively vocal purposes.  I  
have a four-octave range vocally, can sing all parts except low bass  
and first soprano (which would be freakish).

So, I want to be able, in live performance, to lay down loops and  
layer them until I have a full vocal band accompaniment (including  
vocal percussion, although I may consider using a drum machine or drum  
looops).

I want to know what is the best looper for me to buy to do this if  
money were no object.  Then, I want to know the best looper I can get  
to do this for $500.  These are two different questions, I know.

I am looking at the Boss RC-50 primarily, but I want to know what  
people are using to do this sort of vocal looping.  What are the  
strengths and weaknesses of different loopers for this purpose?

I also have a four-voice jazz group that I would like to use loops  
with in live performance, once I have the technique down as a soloist.  
  So, please bear that in mind as you help me figure out what  
equipment I might need.

If this kind of thing has been discussed already, please direct me to  
where i can find it in the archives, or to other sources on the  
internet that I can consult.  Thanks for your help, and "loop on" and  
all that.

Michael C. and the SacTones