OK here's the deal, if you need a better camera, go with the K790a, you can't beat the real Xenon flash on that thing and for me it the deal sealer.
With that said if you don't need to take pictures in bars and nightclubs like I do, the N73 has an almost equally good camera, but you have to live with a much weaker LED based flash for night and dark shots.
Both have decent music functionality. The K790a has A2DP so you can listen using wireless bluetooth stereo headphones. The N73 has a miniSD slot so you can get it up to 2GB and miniSD are more ubiquitous (and less expensive) then Sony's M2 format. The N73 also has a "Music Edition".
Personally, I like the N95 over the N73 if only for the WiFi. The N73 also has the S60 Symbian Smartphone OS, which is pretty decent if you plan to use the smartphone functionality. If you want something more basic an easy to use then the K790a would be your choice. Also the N73 is Quadband which is a factor if you plan to travel and yous your phone in areas with only GSM 900 coverage.
Peronally I say the K790a is the best choice but that's based on my needs. Good luck in finding the right choice for you.