Where sheer production value is concerned, I would have to go with VOY. The colors, the images, the sequence of the frames and the associated music make up a pretty much perfect whole, and it gives you that feeling of grandeur that goes so well with a Star Trek
But overall, I think the TNG opening sequence is the best of them all because it's the most emblematic. It has a very strong and recognizable theme that translates very well into music the spirit of Star Trek
expressed in that famous spoken intro. The sense of adventure and wonder, the drive to "boldly go" and explore. And Patrick Stewart's rendition of that intro gives the whole thing weight and substance. It's burned into my brain.