Practically speaking, the choice is between iOS and Android. Why not try both?
Ask friends to show you how to do common things on their phone and see for yourself what you find most convenient.
The problem with Android is that many makers add their own software to customize the OS. Some find some extra functions convenient, others hate them. But then you're not talking about the OS, but about the added layer, and that's not what your question is about.
Which operating system would I find most convenient in smart phone?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic