Ooh, I love that one.
My favorite two are both in
Endgame, I'm not so sure they count as "smackdown's" but they are good.
BORG: Voyager has entered aperture eight two three, access transwarp corridor zero nine. Redirect vessels to intercept at subjunction (Queen gets an electric shock, voice becomes garbled)
ADMIRAL: Must be something you assimilated.
QUEEN: What have you done?
ADMIRAL: I thought we didn't need words to understand each other.
QUEEN: You've infected us with an neurolytic pathogen.
ADMIRAL: Just enough to bring chaos to order.
Because who doesn't want to push the Borg Queen off of her pedestal.
And then this one, that falls into two scenes.
ADMIRAL: This hub is here. There's nothing in the Alpha quadrant but exit apertures. While you're all standing around dreaming up fantasy tactical scenarios, the Queen is studying her scans of our armour and weapons, and she's probably got the entire Collective working on a way to counter them. So take the ship back into that nebula and go home before it's too late.
JANEWAY: Find a way to destroy that hub. Let's take a walk.
[Corridor]
JANEWAY: I want to know why you didn't tell me about this.
ADMIRAL: Because I remember how stubborn and self-righteous I used to be. I figured you might try to do something stupid.
JANEWAY: We have an opportunity to deal a crippling blow to the Borg. It could save millions of lives.
ADMIRAL: I didn't spend the last ten years looking for a way to get this crew home earlier so you could throw it all away on some intergalactic goodwill mission.
JANEWAY: Maybe we should go back to Sickbay.
ADMIRAL: Why, so you can have me sedated?
JANEWAY: So I can have the Doctor reconfirm your identity. I refuse to believe I'll ever become as cynical as you.
ADMIRAL: Am I the only one experiencing déjà vu here?
JANEWAY: What are you talking about?
ADMIRAL: Seven years ago you had the chance to use the Caretaker's array to get Voyager home. Instead you destroyed it.
JANEWAY: I did what I knew was right.
ADMIRAL: You chose to put the lives of strangers ahead of the lives of your crew. You can't make the same mistake again.
JANEWAY: You got Voyager home, which means I will too. If it takes a few more years then that's-
ADMIRAL: Seven of Nine is going to die.
JANEWAY: What?
ADMIRAL: Three years from now she'll be injured on an away mission. She'll make it back to Voyager, and die in the arms of her husband.
JANEWAY: Husband?
ADMIRAL: Chakotay. He'll never be the same after Seven's death, and neither will you.
JANEWAY: If I know what's going to happen I can avoid it.
ADMIRAL: Seven isn't the only one. Between this day and the day I got Voyager home, I lost twenty two crew members. And then of course there's Tuvok.
JANEWAY: What about him?
ADMIRAL: You're forgetting the Temporal Prime Directive, Captain.
JANEWAY: The hell with it.
ADMIRAL: Fine. Tuvok has a degenerative neurological condition that he hasn't told you about. There's a cure in the Alpha quadrant but if he doesn't get it in time. Even if you alter Voyager's route, limit your contact with alien species, you're going to lose people, but I'm offering you a chance to get all of them home safe and sound today. Are you really going to walk away from that?
I can't really compare any of the fellows either. Honestly - I just think damn near everyone on every Star Trek is good-looking in one way or another - either through looks or character personality. I suppose I don't want to see Ethan Phillips in full Neelix makeup streak around the set with a spotted Talaxian butt anytime soon, but that's an exception. 
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