Which boss looper?

[champion ruby]

I want a looper I can use guitar and keys with simultaneously. At the moment I am looking at either a RC-20xl or an RC-3.

Now my plan is to mic my amp into the xlr input on the RC-20xl while using the instrument input for my keyboards and output the mix to the P.A. On the other hand I am wondering if I could use the RC-3 for the same purpose and have the guitar going to my amp and keys to the P.A. Is that possible or would a mix of both inputs come from the outputs rather than seperate?

Other than this first query, which is better feature wise?