I prefer android devices to the other mobile offerings. While iOS is very polished and maintains a high level of quality control, I don't quite get the level of control I want over the system. The Windows and HP phones had really nice design , but at the time I used them, I didn't like their app offering.
That said, I'm currently using a Samsung Galaxy exhibit, formally known as the "Samsung Exhibit II 4G". The phone was $200 off contract/ prepaid brand new when I bought it last year, and it was well worth the price. 512 MB Ram, huge rom space, fast 1Ghz arm v7 processor. It only got better when I rooted this device. The CPU is able to be overclocked to 2Ghz, and as far as I know that's higher than the Galaxy S2 (even though the SGE is only a single core phone). My upgrade tree was HTC G1 -> Motorola cliq Xt - > Samsung Galaxy exhibit.