I am giving up my 3GS for the EVO.
I have coverage issues with AT&T.
Like you, I am saving a bunch of money, even with the EVO 4G $10 surcharge.
I also am jailbroken. I admit the iPhone is an amazing phone and when you jailbreak it, its even better. I came from WinMo, had a Tilt and with xda-developers modding your phone is a completely different experience than jailbreaking.
I think the only thing I'll miss is the 32GBs of space to carry my music but then again, my iphone will just become an ipod touch and I am ok with that.
I pick the EVO over the next iphone for screen size, Android (long live an open OS), plan pricing, and overall awesomeness lol.
I am curious what the new iphone is going to have though.