Right now I've decided to just offer the DRM free and the Wii U versions of the game as rewards.
The reason I'm not offering the iOS version is that there's no official way to get download keys for games sold outside of the App Store. I know some other projects have gotten around that but it becomes a HUGE hassle, and would actually be detrimental to the rankings of the game which could hurt sales. I'm releasing the game on a bunch of platforms, and I'm just one person, so I'm trying to avoid as much work that isn't directly related to making the game better as possible.
The reason I'm not offering the OUYA version is that because the platform is not even out yet, I don't know how they would handle giving out Kickstarter rewards. If I'm able to give out download keys for free I'll be giving them to everyone who funds at the $10 pledge and up.