I don't see how non-removeable battery would be a deal breaker when discussing EVO LTE vs. S3...the LTE has an excellent battery, no need to add them ugly extended batteries to it.
I'd go with the S3 tho, the phone is a bit more powerful and is getting better support from the developers. But you can't go wrong either way.CM10 for the EVO is pretty good.
Have you tried it on there?
If so, how is the camera and does GPS work?