Personally, I believe DS9 had the best season, post TOS time.
TNG's first season, while getting a couple of the characters right, was stambled with far too many flawed episodes, and too many bad (or at the very least, uninteresting) ones. Finally, it lacked freshness for the most part, which the show found for itself the next year. Still, its mighty entertaining, in its own weird way.
VOY's first season acted like a TNG-lite show. In fact, it acted this way for the entirety of the show's existance. Despite a mighty good opener, the season lost me in interest, quite quickly. In fact, I was mighty bored for the most part.
ENT's first season was promising, like its premise, but Bragga and Berman just had to ruin the potential fun of the first adventure yet.
DS9 was, on the other hand, mighty enjoyable, with ever lasting power. While not Dominion-themed as the rest of the seasons would be, we get the best introduction for the main characters yet, and some really potent storylines. Like with TOS's first season, this is a season that one can watch over and over, and not be bored with it the slightest. Great fun.
And yes, TOS's first season was, by far, the best first season. It is also my favorite season on all things Star Trek. It was the virgin Trek, truly going where no man has gone before... Boldly.
Overall, TOS, and with a little distance, DS9, are, IMO, the best First Seasons on Trek.