As long as you go with a higher end device, Android definitely. It kills in comparison to customization and user functionality. Sure, iOS has things the Android doesn't (but that doesn't mean you can't find an alternative that does just that and possibly better) 95% of the iPhone market is paid applications. (I think we can make a decision based off just that) Also there are a wide variety of Lucid Dreaming applications such as my personal favorite "Lucid Dreaming App" from a fellow Dream Views member Alexander Stone. It is an extremely advanced piece of software that includes sleep tracking through actigraphy and it even tracks when you have your REM cycles. This application is extremely advanced and may be a bit much to take in at first but after a few days of setting it up it will become one of your favorite LD softwares. Other pieces of software include Lucid Dreamcatcher (A dreamjournal on your Android!) and Lucid Dreamer by Guaranis that plays bineural beats after a set amount of time such as 45 minutes (So you can fall asleep before they play )

I have a Samsung Epic 4G and I am extremely content with it - The performance is like no other, and the screen is just brilliant. Best thing about Android? It's open-source.

Good luck in your decision