I know this topic hasn't been posted in for quite a while. Besides that you've most likely upgraded your device already. But I figure I will post this if anyone happens to read this thread and is in the same predicament.
I've owned both devices. Both the Wildfire and the Nokia N900. I found the Wildfire was much too laggy for my purposes even on Cyanogen Mod. I also found the smaller screen to be a bit tedious at times.
In terms of the Nokia N900. I am not a big fan of Symbian, I prefer the Android O.S rooted off stock firmware. But what I loved most about the N900, was the functionality of the phone, and the various mods and alterations that this handset is capable of. Another thing to note with the N900 is the users ability to install Android as a dual boot when the device is powered on. The Maemo O.S. on this device is a Linux software which I find is an added convenience with this model as of opposed to running Symbian.
If anyone is considering swapping to this device look up the "Nitdroid Project" their project support forums can be found here
http://forum.nitdroid.com/index.phpThe phone also has a custom modded version of Cyanogen that can be installed as well. The only thing I didn't like about the N900 specifically, was the resistive screen.
But it truly is a great phone with decent capacity onboard internal SD, expandable up to 32 GB and a variety of tweaks and mods that can be performed to the handset, as well as ongoing project mods and flashes.
I think a user looking for a more 'raw PC-based' smartphone experience, would benefit from the N900. Someone looking for a more 'tailored and current' data device would benefit more so from Android.
Hope this helped