Betfair- the odds there are always better, you can use it for trading as every match is live in play. Also you will find great prices for the underdogs, not only with 0.2 but sometimes with 1.0 or even more. It is the biggest exchange.
sportingbet- the worst bookmaker for tennis.
William Hill- good casino, sometimes the odds for sportsetting are also good, also great service, they answer the emails very fast.
bwin- great bookmaker with a lot of choices to bet on, but the odds sometimes are not good if you want to win.
Mainly, use exchanges if you want to win real money, and open another account at may be bwin or william hill.