I love the N900--still have 2--but the old, small, dim screen, slow processor and low RAM hinder it too much for me to use as a main device.
The OLED and Billboard app on the N9 are things I will really miss (when I move on from the N9). Those are wonderful and unique features.
That said I will eventually move on, and will stop using the N9. But I will not part with the N900.

N900 is much much much better.
On the N9 you lose more than half of screen space when you want to type something. Very annoying in chat apps when the chat is going fast.
Also, N9 has pentile screen, and borders looked jagged with for instance white text on black.
N900 has 'Retina' screen, before "retina' became mainstream.

Thanks, guys. I'll buy N900

U will be da man!!

Not mentioned here, but relevant in some regions, is that the N9 supports more 3G frequencies. I had an N900 here in Australia, but it doesn't support the 850Mhz frequency used by Telstra (and now other carriers) here. So it was a choice of 2G on my N900 or 3G on an N9. I have an N9.

I also prefer its size to the N900, fits nicer in the pocket, the screen has higher contrast, the built in Nokia Maps/Drive and Nokia Music store, doesn't have a dodgy USB connector. All in all, I prefer the N9 as an everyday phone.

For reference I had an N800, then an N900, then an N9. Had them all pretty much since launch. Hoping I'll be able to get a Jolla in Australia sometime soon ...

How do the GPS'es of the devices compare to each other?

I have no experience on N900 GPS, but I had an E90 before N9 and even though the GPS in it was usable it was fairly slow to lock on and exhibited a lot of variance/jitter.

I own both N9 and N900 (two of each actually) and in my opinion the choice depends on the way you will use your device:

You are looking for cellphone with advanced capabilities (so called smartphone) such as offline GPS with voice guidance, decent camera, excellent notification system (for missed calls, SMS, email , ...) and great single hand usability (even for messaging with swype) -> go for N9

You are looking for a pocket computer with voice calls capabilities, FM transmitter, wifi hacking, complete keyboard -> go for a N900

I made the following choice: my N900 has no SIM since a long time, I do not consider it efficient as a phone. My everyday device is a N9.

I have a prototype n900 what can I do with this?

why not both ?

Interesting thread. I have since moved on but am looking to eBay either my N900 or N9. I think you have all sold me on keeping the N900.