Theatrical edition or the TV version with all the extra footage, even bits where background sets were incomplete, for me. Going back to tinker and affects can be hit or miss, which is as much in the eye of the viewer as it is the eye of the people making the changes and those don't always match up. Sound effects went from boisterous klaxons that command attention to wimpy puny noises that sounded like a drunken rat choking on a piece of cheese that command boisterous laughter instead. Of all the Klingon scenes to cut, the editing for the three ships being digitized/disintegrated was extremely choppy. And yet they kept "Klingon cruiser Amar" as spoken by Starfleet as if they're all good friends all of a sudden wasn't deleted? My memory's a bit hazy... I did like some of the new exterior shots to add reference points, and - especially - the exterior for V'ger as that was sorely missing from the original (the fracas for f/x development causing enough problems...

the f/x shown are fantastic so it's a shame they didn't get to do the exterior V'ger shots...)
Taking this a step further and in a weird direction the way I'm wont to do, would you take the Mona Lisa and draw into the background a colonized Martian backdrop the way an artist from 1950 might see it with oblong domes and all? Or rainbows coming out of three unicorns, proportionally placed to keep the rule of thirds intact. How about penciling in some eyebrows? Followed up with a beard and tail and glowing indigo eyes because it'll look even more artistic and engaging? Maybe it would. Maybe not. Why not just make a copy and change the copy but leave the original archive untouched for historical purposes and what it represents of its time because time and attitudes change and develop over time. After all, what was the underlying reason for daVinci not putting in eyebrows? Creativity? Trying to invigorate a new style for the shaving industry? Did he run out of paint? Did he run out of time, he was commissioned to paint a portrait of Francesco del Giocondo's wife and maybe he did the lack of eyebrows and smirk as a subtle joke because he was encouraged to do it from someone? Anyone have a time machine, it'd be fun to find out what really happened way back when. Until then, moose and squirrel will have to do.
But back to Star Trek in 1979:
No home video recording exists. The 1966-69 show was repeated often and by 1977 looked very cheap. The original Phase II TV sets were rightly discarded for the 1979 movie because they wouldn't have begun to have worked. A ton of money went into gorgeous sets for interiors and exteriors, and it shows. Why not showcase it?
Fans would love it, it does look sumptuous - a feast for the eyes (and every other cliche scribbled onto paper via pen). It is more a tribute to TOS, not because it's a (somewhat refined) mishmash of a few TOS episode plot elements, the execution of the elements is put to the side in favor of lengthy visuals.
(But TMP's actual plot is far lighter than the model of the new Enterprise - never base a movie solely on glossy f/x. But I wasn't much of a fan of the first Star Wars movie either, whose plot manages to be much thinner.)
The fanbase was hyped up to see anything with the Star Trek name on it and the step-up in visual quality, thanks to Star Wars, tied them over. Had the visuals not been impressive, not to mention fan interest in Trek in the late-70s (much like disco music) would not remain forever, there would never have been a Star Trek II.
Thankfully the people they brought in - who were not fans but sat through all 79 episodes to get a proper feel for what made Trek unique - came up with a way to more solidly reinvigorate and add genuine substance back into the franchise.
In other words, I'll sit through them all, like bits and pieces of changed editions, but prefer what was originally made. Then again, the extended version had more scenes of characters doing stuff and not camera pans of giant aluminum models.