I cannot recommend the Windows version of KQ6 over the DOS version.
Not only is the Windows version prone to crashing, but it seems to have some kind of optimisation problem resulting in it running slower than the DOS version (both tested on a decent PC).
The Windows version is also more prone to bugs.
Regarding the character portraits, the high res portraits of the Windows version, in my opinion, doesn’t fit the art style of the rest of the game at all. Rather than prove immersive, they tend to take you out of the game whenever one pops up because it just looks so very different.
The portraits in the DOS version reminds me of those in KQ5 and some of the QFG games, and fits the graphics in the rest of KQ6 perfectly.
The bottom line is, KQ6 DOS CD runs fine through DOSBox, and remains a class game, and I would recommend it over the problematic (though this could depend on your setup) Windows version.