Evo has the bigger screen, more "free" apps, and a good reputation for hardware build quality.
Iphone 4s will have a dual core processor (faster), and the iPhone operating system and the little apple logo that seems to make a difference in some people's opinions.
Look into the Samsung Galaxy S "Epic Touch" Spec for spec it beats the iPhone. it has the faster processor, bigger screen, brighter screen, more memory, etc..
If you just care about the Apple logo, nothing I just told you will matter.