Top Spin is probably the only game worth picking up imo anyway.
Virtua Tennis on PC is quite fun, only two types of shot and is more arcadey and is only about £5 or even less in some places.
Top Spin is more realistic and you can play many types of shots: flat, top spin, slice, lob, risk and drop shots. The career mode is great, only downside in my opinion is that the game doesn't have enough top players, only Hewitt, Sampras and Robredo on the men's side. Which is why I can't wait for it on the 360 because then it will have Federer, Coria, Henman and Roddick etc.
But yeh, buy Top Spin and/or Virtua Tennis.