You won't feel a difference between the Duralast brand, or Optima, other than the sting in your wallet. As long as they are Gel-Cell, Deep-cycle batteries, the difference is negligable and more dependent on your maintenance and driving than the battery itself.
I did Car Audio/performance for 9 years, and have always had issues with GM's batteries. Sold Optima's and SVR batteries by the boatload to frustrated customers, sick of dealing with a 90 year old Acid/lead core battery design.
Sears, Autozone, Pep-Boys, as well as a slew of other vendors will be able to get you a great battery. Now if it's like $60.... I'd say you're just wasting your money, but a good battery will be $90-130.