I have had the Evo 4g since a couple days after the release.
Also, have a couple friends and co-workers who have the iPhone 4.
The Evo has been awesome. Sprint coverage is solid in my area, and will be enhanced (to what degree has been debatable) by 4G coming to LA/OC area sometime this year. Battery life has met expectations. I am able to use the phone when fully charged all day - probably 16-18 hours, by the end of the day the state of charge is around 20%. I then charge overnight. I do use BT when in the car, and occasional WiFi/GPS, so that will change the state of charge a bit from day to day.
The screen size is mind blowing. It does make it a large phone, but it is not an annoyance to fit in even my jeans pockets. If you do wear super emo jeans, then it may be an issue.
The camera on the phone is fabulous - the 8 Megapixel rear one at least, I haven't messed with the front facing one too much.
I haven't yet rooted it, but I can give more feedback on that as soon as I do it, to see if and what improves.
As for the iPhone 4, it is a more aesthetically pleasing phone for sure. "You can kill a hooker with that stainless steel case"...or so that Funny or Die skit on You Tube claims
I think that the new iPhone4 users I've talked with are fairly pleased, but they have expressed some displeasure about signal strength based on how you hold it, etc. as has been widely reported in the media...but that is not really a huge deal at all.
Overall, I think anyone going with either phone should be happy....at least until the Droid X comes out...then the iPhone 5, then the Super Evo 4GS or whatever is down the pipe.