Yeah, oddly, I usually find myself gravitating to the plasma pistol as my default utility weapon. (And the human pistol, naturally, though it's not so widely available.) I like the perfect accuracy, the high rate of fire, and the slight stun effect on Elites.
Kara -- Dark Hunter is right; the key to the T&R sword elite room is the sniper rifle. Keep a few dozen rounds handy and practice your no-scopes. I can usually do it first try.
And, yes, I usually ditch the AR as soon as possible, in spite of its pleasant aesthetics. (Even in Halo 3 I'll usually grab something else.)