Frankly, instead of asking us to convince you to buy a phone, you should convince yourself because it will be your phone. You will be the one who is using it for the next year or so, not us.
With that being said, I like the large screen size on the X. In the mobile device world, size does matter

. But the advantage pretty much stops there. I really do not like the look of the X, especially the 4 little rectangle hardware button at the bottom. It looks cheap to me. And when I was playing an X in the Verizon store, those buttons wiggled. It is never a good thing when some parts of the phone are wiggling. But of course, different strokes for different folks. Some people like the look of the X. But I don't.
The Super AMOLED screen is just stunning and there is no equal on the market right now. The hummingbird processor is faster than snapdragon and TI processors. You are free to install custom ROM on a Galaxy S phone but you cannot do the same on the X or it will become a brick.
The battery life of the Fascinate has to be better than the X because the Super AMOLED screen is more energy efficient. And the large screen on the X has to use more energy.
Samsung seems to be putting their financial and technological muscle on the Galaxy S line. So it should be good as they are the number 1 electronic manufacturer in the world, surpassed Sony. They don't become number 1 by producing sub-par products. On the other hand, Motorola Mobile Division was up for sale not that long ago, and nobody (I mean NOBODY) was interested to buy them. That tells you a lot of the company. Even the little Palm had generated a lot of interests when it was up for sale. So do you really want a phone made by a company that nobody wants to buy?
Last but not least, when you turn on the X, it gives you the short audio of "droid". It might please some macho guys, but it is a turn off to many women.
My advice to you is to go to the Verizon store after the launch. Hold both phones in your hands and decide it yourself.