I recently switched to the Galaxy S2 from the Iphone and love it. The battery will last you a day if you flash the proper kernel's and ROM's.
One thing I recommend is that if you buy the S2, get the International Version (Samsung Galaxy S II I9100).
The international version has much more support in terms of ROM and Kernels leaving you with more options to choose from.
A great source for flashing Rom's and Kernal : http://forum.xda-developers.com/
Just look for the...