It really all depends on your personal preference and taste. I have an Evo but I really miss having a QWERTY keyboard. However, HTC Sense is where is at. I had the chance to play with my Co-Workers Samsung Captivate, which is AT&T's version of the Galaxy S, and I really liked the UI. Its different from Sense, but not as good. The Touchwiz UI, however doesn't pull any punches and is just 1 or 2 steps away from being better than Sense. At least that was my initial impression. Samsung's widgets, like "Daily Briefing" isn't bad either. I mention this because the Epic 4G is Sprints version of the Galaxy S.
All in all, I have an HTC Evo, and I would prefer my Evo over the Epic 4G ONLY because I do not like the way the Epic looks. Its form factor isn't as sleek as the Captivate or the Evo for that matter, even though that keyboard is tempting. So, in the end, its all up to you, my friend.