Red Top for my C6 from Tayna. The say they are the cheapest and will match any price. Careful though, a battery might have/be advertised with one of several part/serial #s. With the 2nd one I bought from Tayna, the identical battery was cheaper on Ebay advertised with a different part/serial #. I called Tayna and they refunded the difference.
Also, on the 1st I ordered, the battery sat in a red plastic tray in the box. Thought that was packing material and was gonna throw it away. Not so, it fitted perfectly in the battery tray of the car, and stopped the battery moving around. On the 2nd one, it didn't have the plastic tray (?) so just (re)used the 1st one.