Depends on what your usage is. My wife has an EVO and I have a Vibrant. The Vibrant is clearly brighter and the colors are nice, albeit over saturated from time to time. However, text on the EVO is clearly sharper and easier to read, not to mention the EVO can display more of it since it has a larger screen.
For us the price plan discount didn't make any difference since my employer provides a good Sprint discount so both plans came out about the same on monthly basis including the extra $10 for 4g. So depending on what you use the phone more for and what kind of coverage you can get that will determine which phone is more suited to your needs. They're both great phones though so you can't go wrong either way.
Agreed with everything. I mean I'm in a T-mobile family plan, so obviously I'd have to stick with a T-mobile phone, and my top choice, the Vibrant

Now if I had Sprint, it'd definitely be the EVO, for Verizon, I'd say the iPhone 4. It all depends on the person. Honestly, they're all great phones!