I'd say that your options are either HTC Desire Z or Motorola Droid2. The good thing about Z is the fact that the UI (user interface) should be same globally (HTC Sense), while the Droid2 is in US vanilla-Android, if I recall right, and here, in Europe, it's known as Milestone2 and has Motoblur UI on it.

Why did I mention the UI's? Because those are blocking the latest updates to the Android. As far as I can tell HTC has done good work to keep their devices up to date with Android. I don't know about Motoblur but I know this : Samsung doesn't like updating. There was an article about Samsung not going to give an update to the users but rather make a new device and push the newest update to that one. I think this has happened with Sony Ericsson too?

But yeah. I'd say that you should go and try the Z and Droid2/Milestone2 by yourself. Someone moved from N900 to Z and, if I recall right, he didn't fancy the keyboard in the Z.