Not sure about the Epic, but I love my EVO. It took some getting used to. I went from Palm to WinMo to Android, but I came to the conclusion. All phones do the same things, it's just a matter of figuring out how to do them.
They are both Android 2.2 if I recall, so I think it would depend on form factor. I am a little partial to HTC phones since I cam from a touch pro and touch pro2. I use my EVO with a thin TPU case and it still is pretty slim.
I thought I was going to hate the on screen keyboard, but I installed Swype on my EVO and it made it an absolute dream to use. It is actually easier to text without looking at the screen as compared to T9 and a tactile keyboard. (swype is the keyboard that you can slide your finger over the letters, rather than tap the letters individually. It is very intuitive)
The AMOLED screen is a plus, but i am not sure I would be able to tell the diff. I think side by side it may be obvious, but I the size of the screen is what I like.
I think the important thing to remember is that with android, the whole experience can be customizable. I use launcher pro for my home screens, and I have a bunch of widgets that I paid for. I never thought i would pay for apps, but they really do make things easier/better.