This has come up a few times. As a matter-of-fact, if you look back far enough, I think I asked this question here as well.
I am a fan of Meprolight night sights. I find they give a quick sight picture, and transition well from day to night shooting due to the great white outline around the Tri. viles.
I have Mepro's on both my P99 and my P239, and I love them. I have SigLite's on my P226 (basicly remarked Trijicons) and I don't like them as much. While they both look the same in the dark (brightness and size), the Mepro's are better in any other light.
My P99 is a fantastic pistol. I have the .40 caliber (and I am in the minority there, I guess) but it shoots so nicely, I think I literally get more bang for the buck than with the 9mm. I have been using Winchester 165-grain range-grade ammo (from Wal-Mart) and have shot about 200 rounds already. The DA trigger pull is smoothing out some, but not much.
The quality I most like about the P99 is the feel of it in your hand. Not too heavy, grip is excellent. Although the mid-size grip felt fine, I changed to the smaller grip and I feel I have much more control over the recoil. My groupings today seem to agree.
My wife got the S&W 4013 .40 caliber at the same time I got the P99. I have fired both and there is NO comparison. My wife prefers the Smith, though, as it doesn't look as "evil" as the Walther, or so she says