Android 2.1 has just over 50% of the handsets covered. There are phones out there that will never be upgraded to 2.anything, but I'm not sure if any of them are still being sold as new.

The Nexus One, for the short-term, is the only handset that will have relatively quick access to new OS versions. Other handsets, even brand new ones, might have to wait months (or longer) for updates.

Handsets other than Google's own all come with crapware installed on them that you cannot remove, including time-limited commercial/subscription crapware. None of the add-on UIs are fully integrated from top to bottom, so you'll still feel like you're using two (or three) different operating systems. Motorola can't even properly justify nor size their text labels.

When you have a company pumping out 100 different devices per year, you have to figure that their support for any particular handset isn't really going to go the distance.

There may not be any handsets currently available that meet all of Tom's requirements. At least I don't know of any. Third-party software like DoubleTwist may help with the sync aspects though.