I had a difficult time choosing as well, I kept going back to the Sprint store to decide between the two... and what I decided was that both phones are awesome phones, it just comes to down to personal preference!
For me, I prefer the look of the Epic, (between the rounded corners, the buttons on the bottom, and the screen) everytime I went to the store, that's the phone I kept wanting to use......I prefer the physical keyboard (I'm coming from a Palm Pre)....I hope that this will be my transition phone, I like that you have the choice of virtual or physical keyboard, so I'm hoping that I'll learn to use the virtual more, but at least if I hate the virtual, I still have the physical to use.
The slightly bigger screen on the Evo, the kickstand, and the fact that the Evo is already running Froyo, were difficult to pass on, but I think the Epic is a better phone for me.
I'd suggest playing with both phones at a Sprint store, and follow whatever phone you personally like better, I don't think you could go wrong with either phone!
But in reality, I only need the phone to last me a year, and then I can use my Premiere status to upgrade it to a newer fancier phone next year!!
My Epic is coming UPS today, I should have it this afternoon!!!