If you lean towards phone function and abundant apps right now, as well as do not want a keyboard + Nexus may be best bet (do not know for sure, since not real reviews yet that I have seen).

If you favor more web and media function and about 27gb more storage right from the start- N900 is best bet.

Way too early to make opinion on the N900 for apps, since there are not that many yet.

My hope is quality (N900) over quantity (Nexus) in regards to apps. Nexus would kick N900's butt if basing on the next few months or probably further than that.