Super AMOLED screen (16 million colors) blows iPhone 4's retina display completely out of the water, preloaded with Swype (innovative text input), blazing fast processor, access to over 100,000 apps Cons: Everyone will want to steal it because it's so very amazing.
Super powerful, amazing screen, on all US carriers. Great screen and gaming performance. Cons: Avoid the Verizon version like the plague. Bing as a requirement? Shows how closed Android lets itself become in the carrier's hands.
(I have ATT's captivate) Light weight and really fast processor. Great alternative to the iPhone (Jobs is evil.) Android is open and improving quickly. Nice camera. Cons: Takes some learning if you're coming from an iPhone. Typing and overall UX is different than an iPhone but you'll learn.
Beautiful AMOLED screen (arguably better than iPhone retina), snappy processor, 720p video, social hub, 4G and front camera on Sprint (Epic 4G) Cons: Samsung Touchwiz interface over the default Android, Android - less developers and less polished than iOS