I go for L2 Engineering to get the dam built as soon as possible. L2 Culture is the least important to me as it only gets you the sewing hut, which since new clothes cost 5,000 points, you can't afford to use yet. I normally go:
Engineering
Exploration
Science
Medicine
Farming + L3 Farming
L3 Medicine
Culture
L3 Culture
L3 Engineering
L3 Exploration
L3 Science