I initially got the Epic because I was coming from a TP2 and wanted a hardware keyboard. While the phone worked well, I found there to be a few annoyances that made me swap it out for an Evo:
1) I realized I ended up using Swype a lot more than the hardware keyboard. In fact, I barely used the hardware keyboard at all. I also realized that the keyboard would slide out a bit (even do a slight oreo effect) when using swype one handed. Very annoying.
2) Seeing as this was my first android device, I wanted to keep it stock for the most part but root it for a few things (wireless tether, etc.). I guess I just felt a little more warm and fuzzy inside knowing that the hacking community is larger with HTC devices.
3) TouchWiz sucks. The stock dialer sucks. The samsung widgets suck. Esp. since I was coming from a TP2, Sense just made so much more...uh...sense.
4) The battery in the TP2 works in the EVO - I love playing golf so one battery for GPS rangefinder just wont cut it.
5) The build quality feels better with the EVO. More creaking on the Epic. The EVO just feels like a solid device in comparison.
6) Froyo on the EVO, Epic - who knows when (supposedly soon).
7) When using apps from the marketplace - sometimes they dont support Galaxy S phones (for example - Skype didn't work at all for me, but it works on the EVO). I know its a matter of time, but for the time being it appears that the EVO gets more testing from the devs and commenters
FWIW - I didnt experience the GPS issues others have reported with Galaxy S devices. Of course - YMMV.
The Epic does have its advantages of course - better screen, better video recording, better pictures, hardware camera button, UI feels smoother when swiping around screens or scrolling down webpages. It also comes with a 16GB card (EVO comes with
, but for most people on this site it probably wont matter.
I hope my recent personal experience helps. Which reminds me - I need to send in that rebate slip!