I had a similar question and have posted the following on Audiogon but have yet to have any responses.
I know there have been threads that sort of touch on this but not exactly as far as I can tell. I found a response from Darrell from Mach2Music on a previous thread that stated
"1) 2011 Mac Mini > 2010 Mac Mini
2) Stock Snow Leopard > Stock Lion"
So it sounds like the best option would be a 2011 mini with snow leopard. However, as far as I know you can only put snow leopard on a 2011 Mini if you already have a mac. I don't have access to another mac so I am wondering given the choice between a refurbished 2011 mac mini with lion or a refurbished 2010 mac mini with snow leopard which would people suggest I purchase.