Betfair Betting Exchange offers 20% better odds.

You can "back" and "lay" at Betfair.com. When you back a selection you are betting in the same way as you would at a normal bookmaker. At Betfair.com you can also lay a selection and oppose backer's opinions by offering odds against something happening.You can also bet "In Play" while the action is taking place. This is an exciting opportunity to pick up great value bets as the game develops. It also allows you to hedge out of positions with Betfair.