the title says it all.

I'm looking for a new phone to upgrade from my aging iPhone 4s, although I don't have a-lot of money. In that case, these two phones seem like a nice choice.
I want it to be fast, have awesome multitasking, have a great camera, and that it won't need to ask someone if he has a battery pack I can borrow because my phone ran out of juice at 3PM.
I am quite a power, so battery and performance is very important.
Also, I'm running 32GB on my iPhone at the moment, and it's about to get filled up. that's why I need 64GB.
btw, the Asus is the upgraded atom z3580 2.3GHz model, instead of the normal atom z3560 1.8GHz.
So. which one is the better choice?