Kareem, please keep bias posts out of an argument. :3
The HTC EVO 4G sports that massive 4.3 inch screen, but the Samsung Epic 4G's screen is a super AMOLED and just about the same size. In overall color, clarity, and power-usage, the screen on the Epic 4G is better in my opinion.
The EVO 4G has the Sense UI, making Android look sleeker and gives it extra functionality through the widgets. This is going to be a personal preference, but I personally hate the TouchWiz UI on the Epic 4G. It gives too much color and not enough detail.
The Epic 4G has a full slide-out QWERTY keyboard, giving it an edge in text input. It can also use an onscreen keyboard if physical input isn't your thing. The EVO 4G on the other hand, relies solely on the screen, so that might be a loss depending on how you like to type.
Speed on the Epic 4G is slightly faster due to the architecture of the Hummingbird processor. It is also faster and video encoding and decoding.
Camera quality is about the same, but the EVO 4G has an 8 megapixel camera, making it a more pixel-dense image in a way.
Overall, it depends on how you like to use your device. If you're willing to give up one feature for the other, the other phone probably has it.