First, there is the consideration of sheep versus cow 's milk. Traditionally, feta is made from sheep or a combination of sheep and goat's milk. In addition to providing a more complex flavor profile, there is some interesting research that suggests that sheep milk's molecular composition is easier to digest than other dairy. That said, not everyone enjoys the flavor of sheep's milk, making cow's feta a good alternative.
Another determining element when selecting your feta is its packaging. Unlike the United States, where a majority of feta is distributed in 8oz vacuum packed plastic or pre-crumbled 4oz plastic tubs, fetas in Greece are displayed in the large tins or oak barrels in which they have been aged, as pictured above. Traditional barrel aged fetas are most easily found at Greek import shops. In addition to tasting delicious, they are often priced more advantageously than those sold at traditional grocery stores.
When storing your feta, be sure to either keep it in an air tight container or submerged in a salt-water brine to ensure that the cheese does not dry out. Also, avoid storing your feta in the freezer as this will alter the consistency of the cheese. The good news is that freezing isn't necessary as feta's high salt content allows it to keep for many months if stored in a cool place.
Whichever feta tickles your fancy, what matters most is appreciating that there is more than one type out there. So enjoy tasting and sampling, that's half the fun!