I have the HTC Evo and love it. I don't live in a 4g area but still love the phone nonetheless. Yes, you do have to pay an extra $30 on either phone to activate the mobile hotspot. Both phones have that capability. Both phones have a 1ghz processor. The Evo has a 8 megapixel camera and 8gb included memory and froyo 2.2 operating system as well as a micro HDMI output. The Epic has 16gb of memory included, a 5 megapixel camera and 2.1 operating system. The epic does not have an HDMI output, it does have DMNA which the epic does not.
Also the epic has a 4 inch screen where the evo has a 4.3. And yes, the epic does have a slideout keyboard which could be nice.
Both have Wifi capablities as well. The epic is supposedly coming out with media thing where you can rent or purchase movies through your phone.
I went with the EVO for because I wanted the HDMI output mainly. It's a wonderful phone. Truthfully either way you go you will probably be happy, it's a matter of preference. Not sure about the epic, but it you do go with the HTC my only complaint, (which is a standard complaint from about everyone) is it is a battery hog. Buy a car adapter and keep a charger handy because it sucks the battery down pretty fast compared to any other phone I have.