Captivate has the better SAMOLED screen, with next gen multitouch sensors (ATMEL MAXTOUCH). These sensors can support up to 16 points of contact, but was toned down to 5 points on the Galaxy S devices. While you probably won't ever need 5 fingers on the screen, the ATMEL Maxtouch sensors are the best. Couple said sensors with the SAMOLED screen (which has no air gap between the glass and display), and you have one of the most sensitive screens on the market. It also has one of the fastest, if not the fastest chipsets available on any mobile device thus far. The only con, as you've pointed out, is the lack of flash and lower megapixel camera. Other than that, there really is no competition between the X10 and Galaxy S class phones.
Sony Google TV (NSZ-GT1)
AT&T Samsung Galaxy S3: CM10.1 Nightlies
AT&T Samsung Galaxy Note: CM10 stable
Asus Transformer Prime: CM10 Nightly
iPhone 4: Stock
Motorola Atrix: Cracked screen + MIUI