Yeast

There are two types of yeast on the market: liquid (or pure culture) yeasts and dry yeasts. Both have their advantages and disadvantages.

Dry yeast is inexpensive, convenient, hardy and does not require a starter. But many dry yeasts are also poor fermenters, produce a lot of undesired "off-flavors" and can never be as pure a culture as a liquid yeast. The selection of good dry yeasts is also quite small, and therefore limits the range of possible beer flavor profiles you can get with the yeast.

Liquid yeasts are pure cultures or blends of pure cultures and come in a extremely wide range of choices allowing a lot of possibilities when it comes to affecting the flavor profile of your beer (and if you want to make a lager, liquid yeast is your only option). On the other hand, the liquid yeasts are more expensive.