I was very torn between the Fascinate and the X too, even after I had my X. My Lt. at work has the ATT Samsung Captivate so I've had ample time to play with one. The Samsung phone is excellent in my opinion. The phone seems just a tiny bit faster than my X (almost unnoticeable) and there's no comparison when playing games or watching HD CG videos. The Samsung absolutely blows the X away as far as the GPU is concerned. The screens are give and take. The SAMOLED screen looks AMAZING for nature/scenic things, but to me, people look kinda orange and the whites have a blue tint. The X has more accurate colors in my opinion, but the Samsung has truer blacks, kinda like the difference between plasma and LCD, but even though SAMOLED is supposed to be the top, my preference goes to the LCD in the X. The battery life on my X is actually better than the battery life on his Samsung, we work together for 24 hours at a time, so we've had time to test it, and the X typically gets 4 or so hours more life before needing to go on a charger.
The biggest difference between the two in my opinion is the attitude of the two companies. The bootloader on the Samsung has already been unlocked, and Samsung isnt fighting with the Android community, sending C&D orders like Moto is for the X. This alone would be enough to sway me over to the Fascinate, but I'm waiting to see if the Samsung gets very many developers behind it. The cracked bootloader is great, but it's essentially worthless if nobody is developing custom ROM's for it lol. So for now I'll be sticking with the X, but keeping my eye on the development for the Fascinate, and if enough of the right people start cranking out hacks for it, I'll probably sell my X and buy one full retail.