Suggestion: why not have both? Based on your post, you have used the N900...is it still with you?

And yes, you can still install NITDroid (Android ported to N900 or N9). The NITDroid version on the N9 is Ice Cream Sandwich, by the way. Easy Debian is now also available for the N9. Here's the link to the thread: http://talk.maemo.org/showthread.php?t=85878

As to "which is better?"...you may end up missing the hardware keyboard that we all loved on the N900 (it depends on your preference though).