What is the best use for my Great ppl?

[Aeson]

Depends on which GP you are getting, and what your goal is.

 

[Vizzini]

While I haven't had the chance yet to do this there is a tidbit in the manual I found most interesting.

You can instantly end any and all resistance in a city if a Great Artist creates their Great Work there. If you have a surplus of Artists send them along with your army.

Capture a big city near the opponents core and on the same turn end all resistance there?

Oooooh. Shiny!