Collect Taxes - it increases an amount of money you collect during the year. Despite pretences it isn't a good choice, because chances for steward being robbed are much bigger than the chance for collection the money.
Oversee Construction - it accelerates greatly the speed of constructing the buildings. Particularly useful with the most advanced structures form which some requires dozen of years to be completed. Another plus is a fact that steward may meet the great architect. But there is also a danger that during the works something will go wrong and constructing time will be longer (fat chance for that).
Research Economy Tech - increasing the speed of researching inventions connected with the economy in the chosen county. It brings profits slowly but there is no risk connected with that.
The most important feature: Stewardship