My roommate and I have been playing this game for years and have no clue what civ is OP. come on there has to be one right?

Nope, cause one way or another it's possible to smash face with them all. Though I'm sure there are some that are just garbage.

I think top tier is probably Britons, Byzantines, Chinese, Franks, Teutons, and Vikings.

for 1v1s, the top tier is Aztecs, Mayans, Huns, Persians, Chinese, and Mongols.

Vikings are #1 for water maps.

franks are quite bad in 1v1s but are good for team games. Vikings are pretty bad on land maps. there's no "best civ" though.

Mongols are pretty awesome in imperial and early on . Their castle unit is excellent and if used properly they are a pain to deal with. Celts have awesome siege and their wood cutting bonus is pretty sweet. Persians are scary as hell in imperial and very good in earlier ages.

Saracans are pretty awesome as well. Their ability to chew out any cavalry unit is quiet awesome and you can switch to guns if enemy goes infantry.