I'll be honest, oatmeal is a little more work than some of the other resists (primarily in the wash-out), but it creates a truly unique look. You can achieve the signature oat-y crackle or a variety of marbled, wash effects. I didn't realize it's versatility until I tried a few variations on the basic technique. And of course it has the benefit of being inexpensive and readily available. The other thing I love about oatmeal is that it is very forgiving. Almost any variation in the oats to water ratio or in the amount of time it stands before using will produce good results, as will any method of applying the oatmeal.
Read my tips for working with resists.
Read about working with sugar syrup resist.
Read about working with acrylic medium resist.
Read about working with flour paste resist.