Definitely go with Android. We don't need more demand on the supply chain of N900's, lol!

On a more serious note, based on my own use/needs of such devices:

- If you NEED a particular app found only in certain devices, then your decision has already been made.

- The N900 on AT&T is not as good as the N900 on T-Mobile (in the U.S.) Sometimes, I just need that 3G and don't want to wait for a wifi hotspot.

- I can't live with or without my N900. I wouldn't say it is a love hate relationship since it is mostly love but I really want Nokia Maps on this damn thing and the hate would go away.

If you can't make up your mind, others have already mentioned it, Cheapo Android + N900/N9. I myself am using an N8 + N900 combo, but I just don't want to lug around 2 devices with me all the time.