Oatmeal, grits, and wheat farina are all good. Pick your poison.
For reasons of performance, the answer would be contingent to how your body responds, the event you are participating in and so on. It's just a common sense thing.
E.g., if you are doing heavy weight lifting, say squats, a very fast carb can be good, or for glycogen upload post workout, very, very, very, fast carbs can be extremely useful. For an endurance event, however, a slow carb, placed in fat, may be a much better choice for performance.
The poster did not qualify his question as to event, sport, body type, goal, and so on, so it's impossible to give a qualified reply.
In general slow carbs are better, the differences between grits, oatmeal, and farina aren't that much.
If the poster or anyone else is interested in the glycemic indexes, google can point you to a variety of resources. As well, the USDA PCS 20 food calculator will provide extensive nutritional information so that a person can decide how to tune their diet towards their particular activity.
I personally would lean towards oatmeal as the more healthful of the three, because it provides soluble fiber, carbs in an unrefined state, and a bit of good fat.