iOS started off with by far the best selection of games, just as they did with apps. However, once Android became more common and secured a much larger marketshare, all those same apps are now in the Market. However, at this point in time iOS still was king of game variety, when you exclude the possibility of emulators on Android as they are not available to those who don't know how to root.
In 2012 that all changes with major additions coming to the Android gaming space.
1) Playstation brand is already making major inroads to Android this year with the inclusion of a Sony Playstation Suite and its many games as well as other content. A lot of which is exclusive to Android.
2) GREE Brings Major Gaming Studios To Android – Capcom, Konami, Square Enix and Sega All On Board. This introduces a slew of 3rd party games into Android's universe.
3) OnLive Officially Announced and Now Available For Android – Brings Full Console Gaming To Android Devices. That's right now ALL of onlive's content, which is really nearly all 3rd party games on any system or PC, will also be on Android. (granted this will eventually probably be on iOS and WM as well)
At this point you not only have all 3rd party, but a good portion of Sony first party too (something definitely not on iOS or WM). This console level of play combined with all the regular mobile offerings definitely pushes Android well into the forefront of mobile gaming.
All you need to do is snag a Wiimote or other bluetooth enabled control pad and you have yourself an instant console. Hell, given that most of the phones and tablets can easily output to a TV, you have the best of all possible worlds.
