My 2c:
KoF99 Dream Match - Eww. Didn't like it, must be because I play lots of KoF98 on Neo. It does not feel accurate, some of my fave combos with Ryo, Goro or Joe don't work if timed like on Neo.
KoF99 Evolution - Nice port. The 3D backs are debatable, but Evo feels a lot better than Dream Match. AFAIK, there are issues with anim cuts, but don't quote me on that. You can also link your NGPC KoF R2 to KoF99 Evo and upload extra strikers.
KoF2k - Devil_Gans said it already, it's rushed and incomplete, and the slowdowns can get really annoying. Puzzle mode is nice if you are into those things. It also contains a selection of classical KoF backs from 94 - 99 useable in 2P games, but IMO, they did not make a good choice with some of them. No Pao Pao Cafe?! Ha.
KoF2k1 - Better than the 2k port, but somehow, Playmore managed to tone the whole game down even more. IMO, 2k1 DC is much easier than the original, even on 8. This sucks, but fighting against Igniz is a lil' more interesting in the DC version. You can actually FIGHT Igniz on 8 without resorting to cheap crouch+big jump tactics. The puzzle fighter mode is cool, better than the 2k one.