As you may know, it varies from time to time.
Right now, it happens to be the C-182S. I'm not sure why, though. To be honest, since I've been working on my real-life CFI, I haven't done much more with FS than throw the 182 on autopilot and just watch it fly (I did that for 15 minutes this morning.) Sometimes it's fun to take it bush flying too. Suffice to say, I'm really more into the light, single-engine aircraft in FS2k2. Maybe it's because that's where I'm spending most of my real-life energy, and have sort of forgotten that the rest of the aviation world exists.