I've bought a couple of Anker batteries in the past for my Sensation and G2x, and I have to say they work pretty well. The most noticeable thing is that they don't get as hot, but they don't have temperature sensors, funny.
I would definitely go for Anker, although they make me worried sometimes because they are making these batteries in a Chinese factory...and I'm just not used to the idea of Chinese-made products working well.
Current Device: iPhone 4S (White)
Current ROM: Not Applicable
Current Kernel: Not Applicable
Previous phones: iPhone 4 ---> Galaxy S 4g ---> HTC Sensation ---> LG G2x ---> iPhone 4S(current)
I want to kiss you.....