I have a small site for gambling reviews. For me the best site for betting on sports is Betfair.
Here are the benefits of using Betfair sports
Better odds- As you are betting direct with fellow punters at Betfair there are no hefty bookmakers' margins resulting in odds that are on average 20% better.
Most of the online bookmakers reduce your stakes or close your accounts if you are successful. In Betfair your stake will never be reduced. They never close winning accounts. There are no limits. You can bet without worrying for limits.
Live in-play betting- You can bet almost on every single event live.
Safe and secure- Betfair has over 100 000 active customers a month placing over million transactions a day, making Betfair the World's number one betting exchange. The transactions in and out of the account are fast and secure. You can deposit or withdraw at any time.
Watch live video of many events(mainly football and tennis)
Credibility- Betfair were awarded the Queen's Award for Enterprise in the Innovation category in 2003. Betfair hold Memorandum of Understanding's (MOU) with multiple sports organisations around the world helping to ensure fair play.
Back and lay- The most important benefit. When you "back" a selection (be it an individual, a team, horse, dog or other), you are betting that it will win. This is just like betting with conventional bookies. When you "lay" it, you are betting against it winning. For example, if you're betting in a market on which team is going to win the Premiership and you lay Man Utd, you offer odds to other punters who wish to back Man Utd. If Man Utd don't win, then you pick up the backer's stake. If Man Utd win, then you pay out. This is what bookmakers traditionally do. Back and lay creates many new possibilities. Many new tactics.
You can also visit my review of Betfair at my site http://bettingwise.hit.bg/Betfairsports.html
and get a 35 euro bonus for new players