I'm also in a huge dillema right now what to replace my N900 for good.
But there isn't any that can do the things I do with my N900 right now.

1. MicroB + HW Keyboard - I love the virtual cursor also. It makes it more desktop-like than any other imo. Also love that it supports greasemonkey. I've used iphone/android/symbian and tried many web browsers. But nothing compares to the experience that N900 with MicroB gives. Nothing.

2. Multitasking of videos - Can any other phone do this?? I use SiB + mplayer for playing videos and it allows me to let it play it in the background while I check my email/browse web. Same for youtube videos within MicroB.

3. xterminal - Dunno. I just love performing all the file management and scripting installs, uninstalls etc from the terminal.

4. Multitasking via camera key - I don't think there could be any other phone as quick and easy to multitask naturally as N900+Maemo5.

Most good Android devices do not have hw keyboard which is major fail in my books.
Those that do have one have lower specs and smaller screen sizes. Grrr.
I want big screen, hw keyboard, good video playback support and good web browser.

GAWD. I just wish Nokia made a dual core, bigger LCD version of the N900 with the same Maemo5! (with HD video record/playback support)

Some that do interest me currently are:
1. Dell Venue Pro - Big screen, hw keyboard, wp7 has good potential but will need to wait a while for the Mango update.
2. Samsung Galaxy S2 - no HW keyboard is a concern.
3. LG Optimus 3D - OMAP 4430 is a beast and has interesting 3D capability. (novelty factor)