I went to a Nexus 4 a few months ago. Lovely phone. It doesn't have any extras on top of Android so is nice and clean and Google seem to provide updates regularly. I'm also on a SIM only contract and the overall cost is significantly less than going with the so-called "free" phones on contracts...

However, I killed it (dropped it corner first on a hard floor and the screen shattered). I went back to my N900. I thought I would be frustrated but I actually feel liberated. I feel so much more in control of the N900 than I ever did with the Nexus. Having 'tor' and not relying on Google for anything is reassuring (from a privacy point of view). With thumb, the system is much more responsive. I will be sticking with my N900 for the forseeable future. I only wish it had a bigger screen...