[The Professor]

I've used flaked, rolled, quick, and instant oats at various times.
After a lot of experimentation, I determined that the quick or instant oats gave the best results (and were easier to use).
But any of these will work. 

I wouldn't use steel cut though.  Save those for cooking with dried fruit for breakfast... or to make Goetta (aka "Cincinatti Scrapple")

[erockrph]

I've used flaked, rolled, quick, and instant oats at various times.
After a lot of experimentation, I determined that the quick or instant oats gave the best results (and were easier to use).
But any of these will work. 

I wouldn't use steel cut though.  Save those for cooking with dried fruit for breakfast... or to make Goetta (aka "Cincinatti Scrapple")

Nothing beats steel-cut oatmeal with dried blueberries and some brown sugar. But I agree that they just don't seem worth the hassle for beer. The main benefit for oatmeal is the texture, not the flavor. I can't imagine they'd add anything extra to a beer.