Trying to select different types of episodes:
5. Lower Decks
A simple yet innovative premise: let's focus on the lower-ranked officers for once and observe the main crew through their eyes, beautifully executed.
Characters we barely knew (or didn't know at all) are swiftly devellopped and, by the time of the climax, we actually care about them; turning this episode into a real tearjerker.
4. The Inner Light
When Trek delves into more poetic ventures ("DS9: The Visitor"; "VOY: Blink of an Eye",...), it usually hits the mark and "The Inner Light" is no exception.
A pretty thought-provoking episode, and one that lacks neither in emotion nor action.
2. Who Watches the Watchers
Smart writing, shrewd treatment of a delicate matter, engaging plot, no shortage of actual suspense, a real treat.
1. The Measure of a Man
So many themes evoked in one episode! So many allegories and layers! So many quotable lines!
Definitely some of the best writing shown on Trek (and on TV in general), expertly delivered by all involved, most of all Sir Patrick Stewart.
Ok, ok, I failed to pick different types of episodes, that's 2 emotional ones and 3 intellectual ones. Well, to my defense, that's what TNG does best, for action and humour, DS9 is where you look.
I would've needed 10, tbh.