That depends on what area you are in and what you are primarily using the phone for. The K800i has the best camera functionality because of the autofocus and xenon flash. It's also 3G, so if you are in an area that offers that service, that's probably your phone. I'm in the US so the 3G is of no use to me, so I'd have to get the K790a.
The Nokias are pretty solid phones. The N-Series phones have the symbian smartphone OS. The N73 has a good camera, almost on par with the K800i, but no Xenon Flash.
The N80 has Wifi Capabilities and a large screen. If you like Wifi of the n80 however I'd wait for the n95 to come out. It has the same slider form factor, with a secondary slider for music controls.
