I actually havnt bought a TD game yet (only gotten the free tapdefense and zombieattack1) so which one has more replayability/options?
well zombie attack isnt your usual TD. so if you want a normal TD then go geodefense (the first one) or fieldrunners, if you want somethign different than definately go for zombie attack!
if you want a generic TD game, and are not a hardcore player, get bloons(on easy mode). if you want a hard generic TD, get bloons (on hard mode) or geodefense. it can get hard even on easy mode
the original Sentinel is currrently free, that was one of my first TD games and helped get me hooked on the genre Tower Madness is definitely a TD I enjoy a lot, you can try the full version of that with Tower Madness Zero but it's ad supported
Fieldrunners was a total waste of $2.99 for me. The pace is just ridiculously slow. I mean no fast forward when the enemies move like slugs until wave 75, wtf were the developers thinking?? There were many times my eyes just started drooping watching the enemies micro-inch their way across my elaborate labyrinth, each wave sometimes taking FIVE MINUTES. Get Geodefense or something, it's much more challenging and proper pace.
what are you takling about? Its a pretty fast TD in my opinion. Want a reallly in-depth TD? go for Navy Patrol. They even update it constantly. But aurora here wouldnt like it because the pace is slower than lightning.