You know, ever since I was in like, grade 4, I'd watch TNG with my dad and absolutely LOVE IT. I didn't like DS9 so much once it started; that is I don't recall watching Star Trek every week after TNG ended. I watched the premiere of Voyager and most of its run and I thought it was okay, I just didn't like how cheesy Janeway was. I watched the TNG movies religiously, and I've seen the original movies ever few years since I was just a kid. I was never a fan of TOS, though, other than the movies.
Over the last few months I've downloaded and watched the entirety of Star Trek: Enterprise, and I've got to say it's a damn fine show. The first two seasons were a little over-the-top, but the 3rd season arc was incredible. I watched every single season 3 episode in a row once I started watching the first one. The final season paid good homage to TOS, which it supposedly predated, by bringing up several good issues such as the Romulans, the Augments, and the Klingons. I wish it could've gone on another season, mostly so that they could film a different series finale to replace the godawful one we got with fat Riker and old Troi.
My favorite Trek series:
1. TNG
This is THE science-fiction nerd's flagship show. If you understand the technobabble, you can then begin to appreciate how the focus of each show is on what makes the human spirit such a blessing.
2. ENT
What I loved about Enterprise was how it melded our modern outlook with what could someday be imagined as the atmosphere in TOS, sort of a retrograde '60s look. Scott Bakula still pisses me off, but for what it's worth, I would watch ENT from beginning to end over and over again.
3. DS9
3. VOY
These two series were tied for me. While I remember mostly how cool the Battle of Wolf 359 was in the opening scenes of DS9, I recall watching Voyager get swept away to the Delta Quadrant while I was just a kid. I didn't like DS9 until they brought in Worf and the war with the Dominion, but every random episode of VOY that I saw seemed to be average, nothing else.
5. TOS
I just can't get into it, it just seems so damn campy. Despite how awesome Shatner is, plus the hilarity of some of McCoy's lines.