I am going to only give my opinion for mobile gaming and with that I would have to say the PSVita easily.
I have owned countless handheld devices but one thing always bugged me about them all and that was a lack of proper controls across all types of games, whether they be shooters, rpgs, point and click, etc...
I am one who loves emulation and old school gaming and always wanted my PS1 JRPGs on the go and the closest I got to that was the PSP and my Galaxy S smartphone. Problem with the PSP was the lack of a 2nd analog and the problem with the phone was lack of proper buttons, because touching the screen sucks due to blocking off a portion of what you're trying to look at.
The PSVita is like a dream come true for me, which is why I want it.
I want to mod it. 
iPhone = Great gaming device. Don't agree? Who cares, because you're wrong.
Currently playing:
Final Fantasy VI (iOS), Final Fantasy: Record Keeper (iOS) & Dragon Quest V (iOS)
