I agree in many ways with Don's evaluations of the boards, but he and I also both understand that what features are important to one person are less so to another. I think some of what makes certain features important depends too upon what you would primarily use your board for.

You can get a real good feel for what these boards can do on this forum, but I think the last thing that Don said his post is also the most important as well. I also highly recommend that you to listen to and demo both boards for yourself if at all possible, preferably on a day when you have plenty of time to experiment with both. If you are real fortunate, you might live near a guy like George Kaye or Dan O'Neill, someone who not only sells the boards, but actually knows how they work, and is willing to really work with you, but too often this is not the case.

Having said that, I lean a bit toward the Korg overall for sounds and styles, but will generally agree with Don that the Yamaha seems easier to use. ( In fairness though the PA80 has more functions overall, and like Don, I'm more used to Yamaha's O'S in general ). The PA80 is also due for a major O/S update shortly, which promises to add sampling and some other function add ons as well. To answer your 5 priorities more specifically, here goes my opinion for what it's worth. I own both boards and have them sitting here in this room right now.

1. Both have good very samples and sounds. I
use guitar sounds a lot and in a composition I can get the PA80s to sound more realistic. The other 2 areas in sound where I think Korg wins is on drums and synth sounds. The rest are a tossup for me, ( both excellent ) although I might even lean slightly toward the Yamaha on saxes and on the acoustic pianos. The "pro" factor really comes in the editability, particularly if you like to modify synth sounds. I think the PA80 has the best synth edit ( sound editing ) capabilities of any major arranger on the market, and is comparable to many "pro" workstations / synths.

2. I always thought that Yamaha styles ( even in the 9000 to an extent ) were a bit canned sounding, but then again I play a good bit of jazz and fusion and almost any styles really limit what I can do in those genres. They would work very well for an entertainer playing live to a crowd. The 2000 styles seem a bit better too, than some of Yamaha's other boards. I like the PA80 styles better overall, but one criticism is only 2 fills per style, although with the new o/s there will be 4, just like the in the 2000.
Both pattern sequencers ( for making and changing styles ) are very easy to use for me, and both give good detailed functions.

3. I'm not generally a singer per se, and don't use the vocal functions that often, so I'll defer to what Don and others have said, meaning that overall I think they prefer the 2000.

4. Both are good as Don says. I think he might be right too, the 2000's seem a bit louder, but both produce excellent sounds.
Both boards still sound pretty much the same when I put them through studio monitors or record them, which tells me that the built in speakers offer an excellent accounting to the true sounds that the boards are putting out.

5. Both have very good sequencers for arranger boards, although Korg's will not have editing down to note level until the new O/S comes out. Still, for me, neither will replace my software sequencers. Editing with a mouse and a dedicated sequencer is always quicker and easier for me, but for the first time, I'd have to say I have 2 boards that I can do very useful sequencer work on without having to be hooked up to a computer.

Final thoughts:

No doubt the PSR2000 is an excellent value for its price. Both boards sound good and I'm not willing to part with either. For me, if I want a board that is closer to a pro workstation / synth in features and functions, then the PA80 is it hands down, but at a savings of several hundred dollars, for home use, use as a solo performer, and ease of use in general, you can't go wrong with the 2000 either. I much prefer the joystick over the pitch wheel too. I have had to replace pitch wheels over the years in different boards because I play them pretty hard, but I've never had a problem with the j/s on my Korg M1 after years of use and abuse.

Good Luck,

AJ