If I were going to choose just one antioxidant out of dozens that standout, the choice would be surprisingly easy. Standout antioxidants include vitamin E, C, Grapeseed Extract, Pycnogenol, SOD, Beta-Carotene and a long list of others. Antioxidants do many good things for us, like getting rid of nasties that can be very harmful to our health in the long run. The one I would choose is Alpha Lipoic Acid.
According to the Physician's Desk Reference for Nutritional Supplements, Alpha Lipoic Acid (ALA) has proven use in large, multicenter, double-blind, randomized, placebo-controlled tests), especially for reducing pain, numbness and burning sensations due to Type 2 Diabetes. But the long list of benefits doesn't stop there. People who are pre-diabetic find ALA helps with regulating sugar in the blood, which might slow down or stop the onset of full-blown Type 2 Diabetes. The list includes heart benefits (for clogging of the arteries); energy production at the cellular level; causes vitamin C and E to last longer in our systems; helps get rid of the bad effects of cholesterol; may help with Parkinson's, Alzheimer's, Lou Gehrig's, Huntington's disease and glaucoma. There are 14 studies listed supporting the possible benefits in the PDR.
If you are an old rat, or married to one, then science has proven that memory has been improved with ALA. This could be a way to be sure an excuse of "I forgot to pick up my Mother-in-law" or "take out the trash" just doesn't hold water.
The body can use only so much antioxidant and if you supplement higher, the benefit doesn't improve. But that is just for the antioxidant benefit, ALA does much more. Still, supplementing with up to 400 mg/day seems pretty wise to me. Combining ALA with other supplements can boost the impact. For instance, I like combining it with Acetyl-L-Carnitine for a wide variety of purposes, but especially for heart/cholesterol health. This powerful supplement is not at all expensive and is usually found in 200-mg capsules.