I like the Droid X. In NYC, Sprint is pretty much scoffed at for having poor service by everyone who doesn't use it. For me, it's been solid. Coupled with the lower service plan, the Sense UI over stock Android it seems like a no-brainer to get the Evo over the X.
Oh, and little esoteric things: to me, I like the look and feel of the Evo better. The X is quite nice. The X's buttons function better than the capacitive buttons on the Evo, but the Evo looks so much more impressive. Moreover, the bump on the X is a little annoying. Front facing camera--while Fring and Qik leave a lot to be desired, they're still cool to use video chat.
All to say that I wouldn't mind having either phone, but it's in the little nuances that make the Evo a little better in my book. My 2 cents.