State Property is often the better choice because it's so much simpler to set up. Pre-corporations, switching from free market to SP usually lets you raise your slider 10% instantly, and potentially more, especially if you have a large empire and/or an empire spanning multiple landmasses. SP makes workshops and watermills very strong improvements (esp. with caste system), making pretty much any grassland city capable of spitting out an infantry in 1-2 turns. And you get all this from turn 0. The bonuses of corporations are stronger, but you have to a) wait until you research the techs to found them, b) generate the right kind of great people, and c) spread them, which will cost you a lot of gold. By the time corporations overtake what state property would have given you, the game may well be over.