each of these have their pros and cons. so vote wise

iPhone5
Pros:
-very good user interface
-excellent Apps ecosystem
Cons:
-might be still the same UI
-might not have dual core
-very expensive

Android Dual-Core phones
Pros:
-insanely fast
-good apps ecosystem
-techie, tweak whatever u want
Cons:
-not user friendly for girls

Win Phone 7
Pros:
-nice user interface, thats it
Cons:
-no copy paste (update soon)
-no multi task
-less app
-lacked many basic functionality

WinKia7
Pros:
-better UI than Symbian
Cons:
-many many many
-bye bye Symbian
-maybe bye bye soon for Nokia

Blackberry Dakota