I switched from the incredible to the X. The incredible is a great phone and the UI is more polished. However, between the poor signal/missed phone calls and the really bad battery life I exchanged it for the X. I do not live in a poor coverage area, yet I had several dropped calls in the incredible when I never had a single dropped call on any of my previous VZW phones and blackberries. In addition, with the incredible, I would have about 50% battery by the end of the day without even using the phone. Now, with the X, I have 90% battery by the end of the day and much better phone quality.
In terms of its size, sure the incredible is smaller and fits easier into a pocket. However, any guy out there that gets the X and can't fit it into their pocket - you are wearing pants way to small/tight.