From my experience the Napa batteries are pretty good. Whatever you buy make sure to get the highest cold cranking amps possible. The stock alternator blows donkey balls so the battery has to work harder.
I don't want to speak too soon, but my 10 year old Optima in my Cobra replica has never given me a problem. I do leave a battery tender on it. As for my GT 500, I'll stick with Motorcraft because it's smaller and fits in the battery tray.