I've had my Captivate since they were released, and my EVO for about two months.
In order, my Captivate is my absolute favorite, the EVO is tied for second with my Droid X.
Although I am one who likes a really large display, and obviously the 4.0" display of the Captivate is a bit smaller, it's brilliance, color balance and contrast is far better than that of the EVO. Also build quality of the Captivate is better. Of the four different Galaxy S variants for the US market, the Captivate with it's all metal back, and superbly fitting battery door is far and away the best built.
Other features of the Captivate that cause it to be my favorite, are the consistent speed and long battery life that I enjoy. I have no lag issues, no hickups of any sort. It just works. In fact it's so much better than any of the others is every little area, that overall I have nothing but good things to say about it.
You will notice that I own a lot of Android phones... I'm such an addict...
So the only point being that it's the first hand experience of using each and every one of these on a regular basis, that makes the Captivate such a standout.
If I was to choose just one phone to have (who am I kidding? I've never owned just one phone....heh!) it would be the Captivate.
Cheers...