JenLM: Sometimes the higher concentrations can be a good value; not for me.

I have a wal-mart on the corner that sells 1.5 Gallons of bleach for $2.00. I think it's 6%, but I know it's no less than 5%.
Lowe's, across the street from Wal-mart, occasionally sells 1 Gallon of 10% LC for $4.99, which given the concentration, is actually more expensive than Wal-Mart bleach.
So I've found that, in my case, though I have to carry more bottles, plain ol' generic store-brand 5-6% laundry bleach is just the best value.
The 5Gal 12% carboys that CarlD mentions are available in my area, but they're miles away. And $4.00 per gallon for gas adds to the equation. And they're heavy, too, at 40 pounds each...
A definite intangible upside to the carboys is that they're re-used. My 1.5 Gallon plastic jugs spend 3 minutes in my car, get dumped in, then a pool water rinse, then into the recycle bin.