I have none installed at the time....
but I would do a read up on the P99FAQ page..... Lunde talks highly of Earl's-II nightsights, which sport if I remember Trijicon vials in metal sights.....
other than that I heard plenty of good things about the Mepro's on the Walther/P99 forum.... I guess they have a bigger "white ring" around the vials than the Trijicons for daylight use.......

I don't have them on mine, but personally I like Trijicon.

I have visited Mr. Lunde's fact page a few times (great source of information), and atleast the Meprolight front sight looks much lower on the slide then the Earl's or Trijicon. This would be a plus, since it looks much closer to the #4 sight that comes installed standard from the factory. When I installed my Trijicon, I needed to completely readjust to the new blade height, which is a given. But the Trijicon blade is much highier that a #4.

As a whole, I prefer Mepros to Trijicons. On the P99s I own, I have all stock sights. At the indoor range I shoot at, it is pretty dark, but not dark enough to see the glow of night sights. For me, I like the bright white dots.

I've prev had a Springfield 1911 w/ night sights - except they don't use ones with nice white circles around the tritium. It was a silver circle which U can't see to save your life if its somewhat dark. After that, I just decided to keep the stock sights, even though the better brands of sights do have the white circles around them.

If it ain't broke, don't fix it

I shoot so well with the stock ones that I haven't felt the need to change.