Best Episodes to hook a friend?

[Hypaspist]

I can't remember all the episodes as I have just started a re-watch but memorable episodes for me are:
The visitor (a very character driven emotional episode)
Trials and tribulations (can't go wrong with a TOS crossover)
Way of the warrior (fast pact action episodes)

Each of the above are memorable for very different reasons.

Gotta agree with all three of these. I'd also suggest
"Our Man Bashir," (another great episode that balances between funny and serious)
"Hippocratic Oath" (a good introduction to two of the key characters and the Jem'Hadar)
"Soldiers of the Empire" (if they like TNG Klingons)
"Shattered Mirror" (more of Worf and Garek - Garek totally in character, but Worf is completely different and funny)
"By Inferno's Light" (has lots of TNG style honorable combat stuff, plus it introduces Martok and the Breen pretty well in one episode)