What are some alternatives?
When comparing Bloons TD and Towers of Oz, you can also consider the following products
Fieldrunners - Fieldrunners is a game developed by Subatomic Studios, for Steam/PC, iPhone/iPod Touch, iPad...
Kingdom Rush - Epic game of tower defense available across multiple platforms.
Innotoria Tower Defense - Build, defend and annihilate legion of enemies in this new indie tower defense game
TowerMadness - Tower Madness is an epic 3D tower defense game for iOS.
Bejeweled Blitz - Our games are sprinkled with a whirlwind of smile-inducing awesomeness and polished to a shiny sheen that keeps the world coming back again and again.
Tower Duel - Tower Duel is a Multiplayer Tower Defense Game for iOS and Android.