To make it instant, they just chop it really small so it cooks faster. Nothing's taken out though, it's still whole grain. Supposedly the glycemic index of steel cut is lower than instant but that's debatable.
But whichever kind you choose, it's good for you, so go with the one you enjoy the most (and with the least sugar if possible!)
Cocoa is also very good stirred into oatmeal. Mmmm, chocolate oatmeal! I add a bit of agave nectar and some peanut butter. Yum.


Other people may find things that find in their lifestyle that works for them. Although I'm an odd one, I can eat regular oatmeal soaked in soy milk without heating it up. I think its pretty good but then others like hot oatmeal.