I have both an Evo and Shift. Stock, the Shift in benchmarks, even with being an 800Mhz cpu, benches quite a bit faster across the board.
Cam seems better on the Shift, esp. anyplace indoors where you need flash. Tho the megapixel rating is only 5.1. More doesn't always mean better.
Evo does have a significantly bigger screen which is good, esp for me. I don't HAVE to wear my reading glasses. Evo has the front cam and a kickstand, and of course, the worthless HDMI port. I've never used the front cam, not once. I really don't WANT to see the folks I chat with. LOL
The reason I added the shift to "probably" replace the evo is the keyboard. I type A LOT. Messages, notes, IM's, data from conf calls, etc and it does get extremely annoying to do it with only a soft keyboard.
Sense, for the folks that like it, has landscape capability on the Shift, not so on the Evo.
Phone wise, both are superb. No odd bluetooth dropouts, I was on the phone for exactly 4 hours and 52 minutes today at work, no issues. Clarity is awesome.
Battery life so far, has been better on the shift than evo. Both seem to get the same amt of signal on both 3g and 4G in my house. Data speed tests with 3g, 4g and wifi are very close to identical. GPS seems about the same, nothing odd there.
Right now, the Evo is nand unlockable and fully rootable, the Shift probably will be and is expected, but this may matter to some folks.
The screen on the evo is flush and has been known to "peel" in the corners. Shift is recessed about 1mm, which will probably eliminate the peeling effect that bothers some folks.
The usb/charge port on the evo is on the bottom, which make it easier to hold and use while charging/syncing, but probably makes it more prone to snapping the pins. The shift is on the side, probably stop the damage occurring, but does make it more awkward to hold/use while charging.
Back cover on the evo was quite easy to remove/swap batteries, whereas the shift, attaches really well to where you think you're going to break the clips.
As you see, both have their pro's and cons. All depends on what you're looking for in a smartphone.
In the end, it'll probably be the keyboard over the screensize that will make my decision.