Minsc
Gold Member
Defender Chronicles HD is absolutely the best TD game for the iPad (normal non-HD version for the iPhone obv). It's challenging, varied, looks great, has a Diablo-style equipment feature, levelling up of your main heroes, hundreds upon hundreds of hours of gameplay which is all pure TD presented in a 2D vertically scrolling manner. Beats the utter shit out of every other game mentioned (I'm sorry, but it really does).
Oh and the sequel should be out soon, so buy it too.
I'm looking forward to Defender Chronicles 2 about as much as Diablo 3, it's been a long time coming! It sounds like they took everything up a few notches. That's not to say Kingdom Rush isn't a great choice either. Anomaly: Warzone Earth is pretty nice too, visually great, but not up there with the rest of these imo, much shorter game too.
Also check out Defender's Quest if you want another excellent RPG-TD mix, a little more traditional TD but with some neat features like the ability to target certain types of enemies (strong/fast/slow/first/etc), so your units can be setup a bit more intelligently.