I am definitely going to wait for the epic mainly because of the gpu being far superior to the adreno on the snapdragon chipset. I don't play a lot of games on a cell phone, but if I do it shouldn't be laggy, especially when the iphone doesn't seem to have a problem playing games or scrolling. Despite the fact that I only play a few amount of games on cell phones, the gpu still helps alot in terms of scrolling, web browsing, rendering images/videos, video playback etc. One thing I wanted from my palm pre was to have no discernible lag when scrolling and going through apps and the samsung epic is smooth as butter, smoother than the evo it appears. The hummingbird processor is also supposed to be a little bit better than the snapdragon's.
Second the screen is supposed to be really nice, definitely better than the evo's, so that's a definite plus. The video camera records video in 720p at 30 fps vs only 24 fps on the evo and has much better audio when recording. The camera is also supposed to be better on the epic as well. I also like the app grid list, albeit it looks like the iphone's app grid, it certainly beats the plain one way up-down app list on the evo.
This brings us to another point, HTC sense is probably better than the touch wiz 3.0 interface, htc weather is simply amazing and many of their widgets add a nice flare to the phone. The widgets on the samsung don't come close to the evo's, but since it is android I do see a lot of different customization with different widgets coming out in the future for the samsung. However, I don't see myself utilizing all 7 screens with tons and tons of widgets on each page, I am mainly going to just use a few widgets and go from app to app, so it isn't a huge deal that htc sense is better than the touch wiz interface. I also prefer the evo's larger screen, but hopefully .3 inches isn't a big deal.
-------
What I like about the evo vs epic
Solid one piece unit, build quality is probably better than the epic's.
Kickstand
2 Led flashes (possibly brighter than the one flash from the epic?)
4.3 inch screen
Speech to text (does anyone know if the epic will support speech to text like the evo?)
htc sense
Higher res camera on the front
Where samsung beats the evo
Video camera/audio/picture quality - smoother scrolling/UI performance
Better gpu
Better cpu
Better screen
Better app grid list
----
All in all I'm not quite sure what I want to do just yet, but imo this a comprehensive list of the biggest differences between the two devices. I am going to just need to play with both phones for a while to really see which one I like.