Definitely go for Android, you have the choice of the Web Application (Touch.betfair.com) or the native Android app, which you will need to go to here to download: http://content.labs.betfair.com/android/BetfairNative.apk You'll also need to make sure your Android device has the "unknown sources" checkbox ticked under Application settings)
Also worth noting that WP7 devices aren't getting great press at the moment whereas a lot of the Android phones are getting really very good reviews.
Definitely go for Android, you have the choice of the Web Application (Touch.betfair.com) or the native Android app, which you will need to go to here to download: http://content.labs.betfair.com/android/BetfairNative.apkYou'll also need to make sur