Hat tip to my college buddy Russ for suggesting this one.

Both:

• Come in long strips.
• Marinate well.
• Are tough cuts of meat.
• Need to be cut against the grain.
• Have a strong beefy flavor.
• Come from the cow’s belly area.

Flank steak:

• Is from the abdominal area of the cow.
• Is cooked quickly with high heat.
• Is thicker and wider than skirt.

Skirt steak:

• Is from the diaphragm muscles of the cow.
• Can be cooked quickly with high heat, or slow cooked or braised.
• Is thinner than flank.
• Marinates better than flank.
• Has a richer, beefier flavor than flank.

So, both are long, thin cuts of steak that are tough but flavorful.

But, there is a clear winner here.

Skirt steak performs better than flank in terms of flavor, ability to take in marinades, and it offers more preparation options.

Furthermore, true fajita connoisseurs say only skirt steaks can be used in fajitas; they also work better in stir-fries.