I have never played EUII, but EUIII is an excellent game. From what I can tell, the vanilla release is less historical. However, there have since been two expansion packs which dramatically change the game. The latest (In Nomine) in particular adds a great deal of historical events and options back into the game. EUIII with both expansion packs is easily one of the best strategy games I've ever played. I have also seen numerous comments from older EU fans on the paradox forums which indicates that while EUII is better than vanilla EUIII, EUIII with both expansion packs is better than EUII.