I'm agonizing badly about whether to return my Epic for an Evo.
My main motive for going with the Epic was the slide-out keyboard. Unfortunately, IMHO, the keyboard basically sucks. The keys are too flat and narrow to let me hold the phone GBA/Sidekick-style and type with my thumbs, and it's tiring to hold the phone with one hand so I can use my other hand's index finger to press the keys one at a time. If I set it on a table, it rocks back and forth because the screen is heavier, and I have a hunch that with an extended battery, both of the use cases I've identified that don't involve thumb use will be unusable entirely. So, scratch my big original "pro".
The Epic has an issue with Graffiti -- dot-taps don't work normally. You have to make contact with the screen for what seems like an eternity for it to register as a "tap". I verified this afternoon that the Evo doesn't have this problem.
On the other hand... the Evo's error rate when I used Graffiti was atrocious. HOWEVER... I've pretty much discovered that Graffiti works flawlessly only when you have CPU-scaling disabled (or at least adjusted so it can't keep trying to crank the CPU down to 400MHz or below), and I wasn't able to get the Sprint store's Evo rooted so I could try it. I'm open to suggestions for ways to (at least temporarily) root it so I can install SetCPU and try it in performance mode. This is something I really can't risk without trying it firsthand, because AFAIK, Sprint only allows one exchange to a different phone within the 30 days, so I have to be absolutely, positively sure I'm not going to regret it if I do.
Truthfully, I don't like the Evo's power-button placement... but due to the way I end up gripping the Epic, pressing the button makes the keyboard slide open half the time anyway, so that's another pro I've had to scratch from the 'epic' list.
I'm not sure what to think about the screen at this point. I've heard so many people talk about the Epic's screen as though it were personally handed down from the heavens by the messiah, but I've been kind of 'meh' about it. Maybe if I actually cared about watching movies on it I might be more impressed.
The Epic's remaining pros?
It'll work with a GameGripper someday. As much as I'd love to discount the importance of this, one of my biggest gripes about every phone I've owned since ~2001 has been their dysfunctional game controls. On one hand, I never play arcade games on my phone. On the other, the lack of real controls is basically the reason why. Then again, nobody knows how well the GameGripper will work on an Epic, anyway... the Droid(2) has a different key mechanism, and it's quite possible that the mechanism that works nicely with a Droid(2) will end up sucking on the Epic (or breaking its keys, or being imprecise, or...)
It has a better GPU than the Evo, and uses it. The drivers aren't open-source, but they're a proper loadable kernel module instead of an unusable, unlinkable binary blob like HTC (AFAIK) provides. From what I've read, HTC is up to the same sloppy GPL-violating kernel mischief with the Evo they pulled with the Hero. I'd love to be wrong about this, but I'm not hopeful.
The Epic has a real camera button, AFAIK, the Evo doesn't. A small creature comfort, but one whose lack drove me completely nuts on my Hero. If there's a way for camera apps to repurpose the volume-rocker buttons to use as a camera button, I'll scratch this entire paragraph.
The Evo was several orders of magnitude nicer to hold. Hands down, not even a fair contest.
Areas where they both suck:
* Neither one has real hardkeys or anything resembling a trackball. God, I never thought I'd miss the trackball as badly as I have when I had to try positioning the cursor PRECISELY between two characters in an EditText field without one. Curse both HTC and Samsung equally for this one.
* Both have criminally-undersized batteries. Once again, there's just no excuse for this. If they just provided us with properly-sized batteries out of the box, half the issues and flakiness we have to suffer through would be largely academic concerns for people trying to squeeze two days of battery life, instead of things everyone has to live with if they don't want to (or can't) live tethered to chargers, carry spare batteries, or do without a proper case because none of them fit extended batteries properly.
So far, I'm still tilting towards exchanging the Epic for the Evo, but agonizing badly over it due to the fact that there's no turning back if I do.