Currently this--specifically, the "NEOGEO Mode" that emulates the original home NEOGEO version of The King of Fighters '98: The Slugfest--is the one game for which I'm keeping my PS2 out of storage. : ) NEOGEO mode is a version of the game with relatively responsive controls (only edged out by the PC "Final Edition" version as far as non-Neo-Geo hardware versions go) and rather excellent all-around emulation.
The "Ultimate Match" version has more characters, character colors, and modes, but the new, flashier UI they've inserted into the game clashes stylistically with the old characters and stages, and the new stages they've added are not nearly as well designed as the originals. Also, control input for super moves, at least, is much less forgiving, making them difficult to pull off. (That problem that seems to be corrected in the later "Final Edition" version on Steam.)
Oddity with their implementation of progressive scan in this game: if you have a controller plugged into both ports, you have to hold X and Triangle on the 2P controller, not the 1P controller, in order for progressive scan to switch on. : P (The only other game I've found this in so far is their SNK vs. Capcom: SVC Chaos (entry 434).)