I'm not a big fan of the Trek 3 through Trek 6 props. Nor am I a fan of the general look of the Enterprise through those films. I've always liked the props from TMP and TWOK. Quite possibly because those are two of my favorite Trek films and I was at the right age when they were released.
Of all the classic movies I've always felt the props and the sets from TMP were the most realistic. Just felt like a real ship with real tools.
With that said, it's still TOS that is my favorite, sets and props. The TOS phaser is the best prop EVER!