I had the EVO for 30-days. In my opinion the EVO is aesthetically amazing (I like rounded corners), has an amazing UI (Sense), can be rooted & ROM'd, has a kickstand (should be required on phones of this size) will only get better with updates, and once you get used to the size (in about 12 hours or less), I realized the benefits of messaging, video, and web browsing were worth it.
I like the X because it's on my carrier of choice. I won't lie - I will miss Sense, and although there are apps/widgets in the Market that can substitute, non look as polished as HTC's. However, I believe the build quality is amazing, the screen is gorgeous (as is the EVO's), battery life have been slightly better than the EVO was, it sounds zippier (Sorry, but the EVO - regardless that it has the same processor - just didn't perform as quickly), and I appreciate it's dedicated GPU. The main reason I am getting the X, is because I actually fell in love with the EVO's screen size, and realize I wanted something similar with my carrier of choice.
Nobody, in this forum, that has an EVO should feel like they are missing out. We X'ers and you EVO'ers have really made out perfectly in both cases.