I'm sure everyone here has had to replace one. How I understand it there's generally a Silver battery (2 year warranty) and a Gold battery (3 year warranty). The gold is generally $10 more. I had my battery replaced this weekend. I would have normally gone with the gold, but I had to take it to a mechanic first because the auto store thought it could be the alternator. He told me he put in Interstate batteries because he thought they were the best and it cost $10 more than a standard Gold battery. It was really convenient for him to do it as well.
Anyway, my brother-in-law was trying to convince me all batteries were the same and he just gets the cheapest one. Basically, anytime I make a purchase he acts like he knows everything and tells me I could have got something better for cheaper. I think he's usually talking out of his ass.