“You should never tell the same lie twice.”
(Just saw this ep, so it’s freshest in my memory.)
Do the movies count? If so, then it’s no contest for me:
“If you were any other man I would kill you where you stand.”
But if it has to be from the tv shows, then it’s from the end of All Good Things:
“Maintain position! Mister La Forge --”
Here are transcripts from every TNG episode.
“I will not sacrifice the enterprise. We’ve made too many compromises already. Too many retreats. They invade our space, and we fall back. They assimilate entire worlds and we fall back. Not again. The line must be drawn here! This far, no farther! And I will make them pay for what they have done!”
“VICTORY IS LIFE!”
“TODAY IS A GOOD DAY TO DIE!”
(Battle cries used by a Jem’Ha’Dar guard and Commander Worf as they are about to engage in one-on-one unarmed combat in Deep Space Nine)
“Laddy, don’t you think you’d better…rephrase that?”
Oh, come on.
" … to boldly go where no man has gone before!"
Only because I’ve wanted to say it with the same… method… as Kirk was using as a sort of secondary emphasis…
“I! HAVE HAD! ENOUGH! OF YOU!”
{kick kick kick kick kick etc}
From First Contact, Data in reply to Picard saying he’s about to violate Star Fleet orders.
Sir, I think I speak for everyone when I say. . . To hell with our orders.
“I’m trying to build a computer out of stone knives and bear skins.” - Spock (I might have gotten it wrong.)
“It is… green.” - Scotty (or Data)
The one line I use when something goes wrong at work, “So much for the little training cruise.”
I think that was ‘Insurrection.’ Still a heck of a good line. 
“Excuse me, but what does God want with a starship?”
“Who put the Tribbles in the Quartritcale?”
"A Regulan bloodworm is soft, and shapeless. But Kirk isn’t soft. He may be a swaggering, overbearing tin-plated dictator with delusions of Godhood…but he isn’t soft.
- Klingon captain in “Trouble with Tribbles.”
Most accurate description of James T. Kirk evah!!
“They are not the Hell your whales.”
That’s actually “The line must be drawn HYAH!” Common mistake. 
My choice? Star Trek II. “I don’t believe in the no-win scenario.”
Actually it is qa set of lines… which is also the greatest Kirk Moment:
KIRK: I Don’t believe in the now win scenario… Kirk to Spock it’s been 2 hrs
SPOCK: Right on schedual Admiral
KIRK: All right. (To SAAVKIK) I don’t like to lose.
Jean-Luc:- “Merde”
Highly illogical. :dubious:
“I will be … irritated.”
(Worf’s reply when Riker asks about the consequences of losing at Stratagema before progressing far enough for Worf to win his bet.)