The Kurzweil romplers of the mid 1980s were really light years ahead of the competition, their samples of 1985 sounded considerably better than those of a Yamaha SY99 in 1993.
By now, I think the difference in authenticity between the competitors has decreased strongly. IMO it really depends on the single instrument sampled which of the competitors is most authentic. Kurzweil doesn't seem to have changed much since the late 1990s, so they are in danger of losing their edge (some say their samples sound old already, I don't necessarily agree).
Korg is often criticized, but I have a very good impression of some of the Korg M3 XP expansion sounds. The Korg brass and woodwind expansions that came with the M3 Xpanded had some of the best solo trumpets, saxophones, French horns etc. I ever played, better than those from Integra and Motif. In contrast, a lot of the preset sounds of the Krome lack authenticity. I don't know exactly if any of the great expansion sounds are implemented in the Korg arrangers. So it depends!