Transferwise.com and Currencyfair.com are the only Peer to Peer money transfer companies I know of. All good. Could hardly be better. I haven't compared exactly the same deal on both to see if there is a difference in value but guess it would be very small if so. One difference is that any few pounds of change from a Transferwise deal goes back to my own bank account by default. Last time I used Currencyfair, the £2 or so stayed in my account with them by default, to use next time or transfer back to me.
(Auctionchex.com is something similar too and perfectly good, based in the needs of people who are offered cheque payment in another currency. Their strength is in reducing the minimum charge for paying-in an overseas currency cheque, for example from an ebay sale. I don't know whether they compete the kinds of transfers Transferwise do, and their DIY web site is a bit like my DIY website rather than something slick.)
Back to the subject of Transferwise: I recommend them.
Connect with Facebook to get one click access to Trustpilot. It's easier.
Sign up with Facebook