What I did for a comparison was made two island cities in world builder. I put nothing bt grassland farms on one, and nothing but grassland towns on the other. I let the grassland farms city grow to as big as it could, and put them into scientist. I figured for as long as it would take for the cottages to grow into towns you could probably get an acadamy and 10 settled scientists. Maybe that was low, don't know. At 100% the commerce city won very very easy. From about 80% and below the specialsy city won. I didn't add any of the techs or buildings that would have helped ( rep, printing press, etc. ) I didn't do anything with the corps, because they seemed like they would benefit equally. I usually change farms to cottages after demcracy, and just let emancipation do the work. GP's are more valuable early it seems anyway, and farms are less pillagable than towns, so I prefer them in the early game. It seemed in my test that in the end commerce wins, but for most of the game specialists are most effective. I just think you have to pick a good spot to change.