I am so on the fence as well and just agonizing over the decision. I dumped my Treo 750 on AT&T, don't laugh, and picked up an Epic two weeks ago from Best Buy. I love it. Great keyboard for long or jargon-laden mail, GPS is great, anti-shake camera good, usually excellent battery life (see below), zippy performance, and I like any number of the alternate launchers and widgets out there so Sense isn't really an issue. (although the Friend app sounds neat and I can't believe the Epic doesn't include Daily Briefing.)
YMMV but the weaknesses *I've* experienced are:
1) Apparently zero noise cancellation when calling. People I call report significant background noise whether wind, restaurant, etc. Not sure EVO would be better but neither appear to have anything like a dual mike.
2) Weak vibrate. I can have it in my pants pocket and never notice. I picked up the Missed Call app and that helps because every few minutes it can long vibrate but it's still a problem. Oddly I've seen folks on the EVO forum complain it vibrates too loud.
3) Frequent but erratic slow 3G speeds. I've done all the radio updates so far.
4) Cell standby battery issues. I've seen some good posts on this. The intermittent fix of enabling airplane mode and immediately disabling airplane mode works but I have to monitor the phone and make sure it hasn't started looking for signals again.
5) Less voice coverage than AT&T. I know Sprint has roaming agreements with Verizon, which theoretically means I should have great service, but the phone doesn't cut over very well. I think there are a number of hacks for the EVO to force roaming and there's even an app called Roam Control for HTC CDMA phones. Not sure how well it works, and the app is supposed to support Samsung phones in the "future," but it's available *now* for EVO.
6) Most importantly a limited ecosystem. I know it's a brand new phone and the international only went on sale June/July, but the Galaxy S is fragmented with a world version and 4 different brands in the US. EVO has a tremendous amount of excitement and momentum. They've got a 1-click root, NAND backup, allegedly a solid and evolving Cyanogen ROM, a billion cases, skins, and other peripherals, and it can even run the Swype beta. It just feels like it's a safer bet for ongoing development.
If it sounds like I'm down on the Epic, I'm not and I absolutely love it, but I just can't decide if the Evo is a better or safer choice than the Epic.