We discussed this very topic at some length in
this thread
My personal opinion is that the 3G gives you more options and is more repeatable.
But you lose out on the simplicity and lower intimidation of the 2G. The 3G looks like some crazy weapon on the front of the camera - you can end up with people being a bit more distracted by the lens than the much simpler 2G.
In terms of how they work - optically the same, you can shoot a wider range of stuff with the 3G, but it can be more awkward to use and freak people out more.