One distinction to be made is that there are maps called "conquest maps", which have specific starting points for each player with the rest of the territories on the map starting neutral; The Feudal maps, New World, Peloponnesian War, WWII Poland are examples of these.
I think that's the biggest disctinction to have in mind, the differenence between Conqest maps and non-conquest maps.
A vast majority of non-conquest maps are very similar in gameplay. In fact they are simply just different shapes and sizes so to speak. Then you have those starting to push the boundaries of normal play by adding a capital or two perhaps, and then the madness spreads, lol. You just need to find your own comfort zone, somwhere between a totally standard gameplay map like Haiti, or the organised insanity of Stalingrad
Have fun =)