When selecting a New World commodity to buy land for and then trade for, there are four main agricultural products to consider.
Cotton is valuable as a substitute for wool. If your homeland is short on wool, cotton is a good resource to purchase since you can make valuable fabric out it. Fabric is used to recruit labor, to build ships and regiments, and to sell for a profit.
Sugar Cane is used to produce refined sugar, a luxury product essential to the productivity of your more highly trained workers. Tobacco and furs also produce essential luxuries usually in demand later in the game than sugar.
Of these three products sugar is often the best first choice. Sugar is more common than the others, and the technologies that let your Empire benefit from this luxury are easier to obtain than the tobacco and fur related technologies.
