I'm the planner. This may sound arrogant, but it isn't. I happen to be an expert tactician. Thanks to the military training I had in the RAF Cadets (well, a similar group) at school, I have pretty good skills in various military aspects, that plus my love of RTSs makes me a great tactician. And so I always end up planning a full battle plan and then taking an active role, usually regarding stealth or sniper work.
Now, here's where it might start to sound arrogant (though it isn't). Every time I come up with a plan for a game, and my teammates follow the plan, we end up winning. Every time they ignore me and do their own thing, we end up losing. Coincidence? I doubt it. Sadly I haven't played TF2 as I'm still waiting to get the Orange Box on PC (when I can afford it). At least there, people realise the value of teamwork and a good battle strategy...