Most everyone I know who aren't Star Trek fans will watch Star Trek 4, it is a lighthearted place to start.
Agreed. In my experience, TVH is the most accessible film. It's a feel-good movie that appeals to everybody, not just veteran Trek fans.
Remember, we're not talking here about which movie is best, or has the best music. We're talking which movie works best for folks who don't have a lot of experience with Trek.
I love TUC, but it strikes me as an odd film to use as an introduction, since it's all about bringing the saga of the original crew to a close. Beginning with TUC is like starting with the final chapter and farewells . . . . .