Well sevdali, look at additional things

Things like hardware specs, how much space do you need? Both are expandable with microSD cards. But there's no (official) way to run applications from the SD card on Android yet. You can (unofficially) though. N900 comes with around 32 GB of built in flash memory (more around 27-29 GB after you take out the 2 GB /opt parttition and factor in whether they're counting by 10^2 or not).

Then there's what kind of applications you want to run. How often do you multi-task. Both devices multi-task but the N900 is better at it once you start going above 6 apps.