Personally, I’m not much of an AV whore. The Blurays are passable for me, but I can see why people despise them. Just gonna go on a hunch and say the early 2000s Collector’s Editions are your best bet in general. Also depends on what cut of each film you want.
The Motion Picture - Director’s Edition DVD for that, 2009 Bluray for the theatrical, and you’d be stuck with 4:3 VHS and laserdiscs for the Special Longer Version.
The Wrath of Khan - the new 2016 Bluray is absolutely perfect imo. Has both the theatrical and director’s cut. Just watch out for the first print run that had a mastering error (I never got around to replacing my copy, so I’m stuck with the back of Sulu’s head)
The Search for Spock - Collector’s Edition DVD. Bluray is among the worst in my opinion.
The Voyage Home - Collector’s Edition DVD. Bluray is plagued with DNR.
The Final Frontier - Ditto. People seem to overlook how butchered this one’s bluray is. The ending is the most obvious, when they’re on Sha Ka Ree, it’s a total wax fest.
The Undiscovered Country - 2009 Bluray for the theatrical cut and theatrical framing, Collector’s Edition DVD for the extended cut with a much larger framing. The VHS/laserdisc version is also a tad different, but not by much.
I’m no expert though, so take this with a grain of salt. I’ve also never watched the Laserdisc editions of the films (even though I own them, I really need to get a player).