I'm owning a N900 and N9. My subjective feeling was that the reception of the N900 is better compared to the N9.

I did a testing with both devices and the same sim card. I put both devices on a desk and did some 3G download speed testing (without touching the device).
N900 got 3.5G (but only ~1Mbit download rate).
N9 got 2.5G (only ~0.2 something Mbit).

Wifi reception shows similar situation. In some rooms of my house I don't get wifi reception with the N9. The N900 has no issues in these rooms!

I also had a chance to compare the N9 with a Lumia 800. This was really embarassing. Lumia 800 had better wifi reception compared to my N900 (and of course N9). Also 3G was much better. Doing the same testing as descibed above the Lumia 800 reached ~4.5Mbit without problems). Again the N9 didn't switch to 3.5G at all.

Guys, I don't get it. At least I would assume that the N9 must be on par with the Lumia 800...