I have all STAR TREK series except the animated one on DVD or blu ray.
They all have have some good stuff(except enterprise that I blame for killing of the fanchise)
Why go back in time, you had 21 seasons of TNG universe, so much to build on, the end of dominion war, sneaky romulans ect. THE RETURN OF THE SISKO!!
While TOS have some good episodes, they are reather silly by modern standards TNG, DS9, Voy has held up much better. TNG introduced tuch screen and flat screen we now use.
Voy ended like 15 years after TNG, yet TNG fit perfectly into voy, sure the effects are better, but they still used the same tech.
My favorite episodes of TNG are
1. The inner ligher,
2. To the Nh degree(no huge episode, just a standard sci fi riddel to solve, to me this is what made TNG so great, just lots of good Sci fi riddles.
3. All good things
4. Who watches the watchers
DS9 was ok, but for some odd reason, the suporting characters(like Garak, Nog ect) were more intersting then the main characters(never liked Sisko)
I used to really not like this series, I watched it on tv many years ago, but after I bought the series and watched the enite series in 2-3 weeks, I got a much better view of it.
Enterprise is just bad, bad acting, bad stories, boring stories, boring setting.
DS9 is ofcourse the series to watch if you want to get into the mood of Sins of the solar empire, with it's huge battles.