I played World at War a lot but not as much as I played Call of Duty 3. I really didn't like the controls at all in Modern Warfare Reflex (spent hours trying to tweak the controls to something I could use). So didn't stay with that long at all after I beat it. I played the Conduit the least of all mainly because online multiplayer wasn't doing anything for me. Overall, due to the Wii setup, I haven't clocked in a lot of hours on an online multiplayer recently. When I have my 360 for that, just doesn't do much for me, unless I have a group I can talk with over Xlive and play it then.
HOWEVER, back in late 2007, and early 2008, I clocked in easily over 200 hours (maybe more) on Medal of Honor: Heroes 2 and that is my most played Wii game to date. I still have yet to find a Wii online shooter that I enjoyed as much as that (though World at War was close).