There are several betting exchanges available to bettors, the big 4 being: Betfair, BetDaq Smarkets and Matchbook. Betfair comfortably have the best liquidity across the board, however the others are catching up every day.
Matchbook offers just 1% on all other sports, smarkets also offers just 2% on all sports. 3% can be had on BetDaq (who also offer 0% commission on the first UK horse race of each day, and 0% on the early premier league fixture each Saturday).
I, like many others, have a love/hate relationship with Betfair, their high commission (5%, 6.5% for many non-UK bettors) riles me, but their liquidity and often better odds keep me somewhat loyal. They've mostly lost my footy and horse racing action to Smarkets though, and I gleefully squeeze every last penny out of Betfairs more frequent promotions.
A 25 quid risk-free first bet can be had for new signups at Betfair.
A 50 quid free bet can also be had at BetDaq
Smarkets also offer up a free 10 quid bet for new signups.
A 25 quid risk free first bet is currently available from matchbook if you google around.
