Depends on what you are going for. Lower level governements are better to raise local troops. Higher ones are better to develop the province.

Roleplaying may be another thing. For example the Romans were comparable imperialistic and therefore would prefer higher levels of governements; they also had the means to spread their culture all over Europe.

In some spots I would always start with a level 4 government when conquered by the Romans: Massilia, Syracusae, Kart-Hadast, Athens, Pergamon, Alexandria, and advandce the level later (when the client ruler dies for exampled).