Major John Shepard: All that "dumb flyboy" and then, "On the Mensa test, there was...." Also, hot.  and also: snarky.
Rodney McKay: Absolutely brilliant. Phenomenally, rub-it-in-your-face brilliant, and then, "In case you haven't noticed, I'm a very arrogant man who always thinks his plans will work!" and also: snarky.
Daniel Jackson: He's right. A lot. And when he's not: "Yeah, I was wrong about that." and also: snarky.
Colonel Jack O'Neill: Again, all that "dumb flyboy" act, and then he owns a telescope and loves astronomy and uses the right names for technical things (when Daniel and Carter aren't listening). and also: snarky.
Methos: "I didn't get to be 5000 years old by caring about anyone but myself" -- at the end of a rant about how Duncan should take better care of himself. ("Could have fooled me," was Duncan's response.) and also: snarky.
Spike: "I know I'm not the first choice for heroics and Buffy's tried to kill me more than once. And, I don't fancy a single one of you at all. But... actually, all that sounds pretty convincing. I wonder if Danger Mouse is on." and then "I do remember what I said. The promise. To protect her. If I'd done that... even if I didn't make it, you wouldn't've had jump. I want you to know I did save you. Not when it counted, of course. But after that. Every night after that. I'd see it all again, do something different. Faster or more clever, you know? Dozens of times, lots of different ways... Every night I save you." and also: snarky.

I need Atlantis fic -- long, plot-ful, slashy, McKay/Sheppard fic with good characterizations and better romance than "A suddenly realized B was hella hot"

And by long I mean ~10K words or more

Clearly I've been spoiled by Shalott's fic:
A Beautiful Lifetime Event
Transcendental
Proof by Contradiction