Vietnam!!! That game owns so much! The Hueys in that game rock! My second choice would have to go to Medal of Honor. It's my favorite WWII FPS. Great multi. BF42 would have to be my third choice because it's getting outdated. If they port BF42 to Vietnam... it would own so much. AoE would be my last choice. It really doesn't relate to the other games on your list. AoE is a great RTS though.
Oh, and if you guys are interested in Medal of Honor, Call of Duty, America's Army, or the Battlfield games... you should check out my clan site... -->
www.mcgamers.com