As much as I hate to say it, but WP7.5>Harmattan.

And that's NOKIA's fault, since MeeGo>>>WP.
Also hardware-wise, L-900 > N9.

So no [real] contest that L900>N9.....but I chose "I don't like any of them" because its the most accurate answer.

I'm beginning to like Android more-and-more, I believe 2.34+ > WP7.5 as long as the device is easily rootable, has unlocked bootloader and custom roms. So without the "product value" I would choose the SGS or EPIC 4G over the L-900 easily. The fact that it has the latest Android 4.0.4 ICS and a AOKP port is just extra incentive.

And that's a 1.5year old device!
Now we've got offerings like Captivate Glide, RAZR/Droid4, One S/X, LG 4X HD, Gnex and NOTE....and even better ones like NOTE2 coming shortly.