I am really not sure what this has to do with bitcoin
Generally speaking, prosper is a good platform to invest in if you want to invest in Peer-to-peer loans, primarily because they handle the collection of delinquent loans, and do a fairly good job in verifying the identity of borrowers.
Then contrasts to bitcoin related Peer-to-Peer lending sites like BTCJam, which force the individual lenders to pursue collections of loans, which makes collection much more difficult as collections is something that really needs an economy of scale to be done efficiently.