Honestly it comes down to UI and type of phone. Ask yourself these questions: do you want a slab phone or a slider? Do you want touchwiz or sense UI? That will answer everything there. Those are the only differences I can see as of now, and while the screen is .3in larger in the evo the AMOLED is brighter and more vivid. So really its a tradeoff as both screens are pretty good.
I don't agree with the second criteria on the original ui/skin. Really that is a temporary aesthetic that is present at the sales counter for the smartphone neophyte but not an issue for people who frequent these forums and are more likely than not to change it.
On your first pint I agree, I think the more permanent aesthetic of the EVO's form factor is more fresh, more modern and more appealing to me, but if you want the function of the keyboard, if you do a fair amount of text entry, that form over function is not a good choice.
I think one needs to zero down on other differences from minor to substantial, some of which we know, and some we will not know until a bit after epic release.
eg-
Screens matter:. Al the comparative reviews with the simple hands on are unanimous that the Epic super amoled is markedly superior. The screen is an every increasingly important and dominant aspect of smartphones and their apps, and that is no small advantage.
GPU and video generally: I haven't done comparative tests but I think those who have say the Epic is superior GPU as well which can make a difference in video viewing and almost certainly will be superior for gaming.
Battery: they both have the same battery MAH wise but my understanding, is that super amoled is less driaining and the epic's processor also has a better power efficeny. This is likely (but not certian) to translate into superior battery life for the Epic. We may see identicle numbers for the "standard" ratings for standby and talk times, but those are increasingly irrelevant given they are not even going to take processor efficiency or screen efficiency into account when that is quite large part of what we are using with smartphones.
call quality: My own causal try out (and reviewers also note this) indicate exceptional call quality with EVO. It is still a phone and call voice quality matters -- a lot. I haven't seen reports specifically on the cdma galaxy call quality yet.
Likely userbase size: The likely user base is important. The Epic is served by to some degree by the fact the galaxy is out on two gsm carriers and will almost certainly be on
both major cdma carriers. the evo is popular out of the gate but that could be huge or short lived. this goes to apps optimized for the device and to hardware accessories such as extended batteries (I understand both are using batteries from prior devices so extra batteries won't be expensive.)
Those are my considerations. I will be getting four 4g smartphones on Sprint in early September when I convert my plan. Although I am leaning to the epic, it isn't because of the keyboard or ui, but mostly from the much superior epic display. Availability may actually be the deciding factor if either are in short supply.