It's a battery, 'nuff said.
Majority of staring batteries are AGM now. Apparently you could drain the sulfuric acid out of flooded batteries to make stuff. Think "Breaking Bad". No big deal, AGM (or any sealed) batteries are kewl. No refilling, no acid boil over (corrosion), they just work.
I've been using batteries from Interstate, mostly because they're easy to get from my local hardware store. Both my C-10's have in excess of three years on the battery, though I know they're about due to be replaced... they're getting old (time wise).
Saving ten clams by ordering from the inter-web is enticing, and may be a factor for some people. I tend to buy convenience, even if it costs me a couple of bux more.
And, though I don't have the stats, I suspect there are only a handful of battery *MANUFACTURERS*. The rest are re-brands.
Rick