All of the ones mentioned so far are great, of course. I guess if I have to pick my *most* favorite for each, it's ones also already mentioned:
Jack: The eyebrow raise and abject hope when he says, "But I may be back... If the Army don't get me."
Ennis: The way his face lights up when he sees Jack's truck pulling up to the apartment - I fell in love with Ennis in that scene, too
*Very close* runners-up:
Jack: The look on his face just as the wheels are turning just before he asks Ennis "Your brother and sister do right by you?"
The look on his face after he asks the bartender if he knows "that girl over there," he tells him her Dad basically has a lot of money, and he looks back at her again to see her getting up to approach him.
The look on his face right before he takes that almost spiteful drag of his cigarette while peeling potatoes - kind of in between the sigh and the drag (and I *love* the way the cigarette dangles there. Oh, to be that cigarette...
)
The way he grins closed-mouthed at LaShawn while she "talks a blue streak" on the dance floor
The stunned look he has after Randall says "... do a little fishin'... ya know?"
I could go on all day...
Ennis: The glance he gives Jack right after he says, "My daddy says rodeo riders are a bunch o' fuck-ups"
The grin he gives the Basque after he says, "Too early in the summer to be sick o' soup" (on second thought - that was when I fell in love with Ennis - the face lighting up scene just sealed the deal)
Those black onyx eyes of his on fire and not daring to meet Jack's during the second tent scene
Oh, hell, I could go on all day here, too...