Alternative finance - best returns?

I've been looking recently for "alternative" financial instrument (FundingCircle, RateSetter, Seedrs, Zopa, ...); what's your take on these?

I'm tempted to try RateSetter - the system looks simple enough, and you can withdraw the money in case you need them, making it a "better saving account" (although not guaranteed in case on company's bankrupt). Is there any other instrument/service I should consider?