I have a Droid X and like it a lot, but miss having a physical keyboard like my BB curve before and its larger than the other two which has its obvious benefits and drawbacks.
I have heard that the Incredibles don't get that great of battery life, apparently because it has a slightly less efficient processor and Motorola has very good battery management software. The droid also also don't have the solid build of the X, which has a metal frame. A few weeks ago, I was getting out of a truck and it slipped off my lap onto the concrete and all it has is a little chip in the side where the finish came off and u can see the metal.
Software wise, they all are now on 2.2 (Froyo). Besides that, I don't think they're much different, except their customized user interfaces by Moto and HTC. A lot of people really like HTC's UI "Sense." If you don't like the stock motorola UI though, a different launcher (i use LauncherPro) can be installed that takes over that and they are very customizable and give very similar experiences to Sense.