Well, let's compare!
The original was quite clever, and had some surprisingly deep stories, but there were also the awful costumes and backgrounds. A classic to be sure, but not my favourite.
I started watching Star Trek with Voyager, and I quite liked the premise of a "lost" ship trying to get back home. It gave the writers a ton of freedom, good effects, and the stories were overall solid. Plus Seven was hot, and that skin tight suit...but I digress. Voyager is essentially tied for the spot of my favourite series, but it narrowly lost.
Enterprise wasn't as bad as people claim, but also not as good as it could have been. Given the premise of a pre-federation galaxy, the stories could/should have centered around exploration without the need for any sort of conflict. I like to watch the occasional re-run, but it's not my favourite.
Now TNG, my favourite of them all. Three word: Jean-Luc Picard (or is that two with the hyphen?). If he isn't the single greatest thing to happen to Star Trek since Gene Roddenberry, I don't know what is. Yes, TNG is amazing, although the acting/costumes are a bit weird at times. Whatever, few things top an evening of TNG...