Gachinko Tennis is the best tennis game for Android. You can find it here: https://market.android.com/details?id=jp.mapp.tennise&feature=search_result
I tried Crosscourt and I find that autorun makes the game too easy and turning it off just makes it way too hard. The gestures for running have to be made before you make the gestures for hitting.
With Gachinko, you have a control pad for movement and two buttons for hitting. It makes for a more natural way to control the game. At least, it's more natural for me. I'm used to a joystick on one side and buttons on the other.
Gachinko also has a number of different serves you can choose from. Each subsequent computer opponent is progressively harder and each has a different style of play as well. My only criticism is that some of the serves that the computer player makes seem impossible as they seem to bounce in a totally different direction as you expect.