Out of those three I'd say Unreal 2.
Vietcong runs like a mule on most systems (not mine
) and isn't very interesting, other than the dialogue which is absolutely hillarious.
Red Faction II is pretty useless, part 1 was ok but 2 is total meh-age.
Unreal 2 isn't the best either but it does sport fantastic visuals and some very cool gameplay moments.