It really depends on how you treat them - a decent battery in a street car that never goes off road, doesn't see rough roads, is the right size or larger, is paired with an easy to start engine, has good thick cables, connectors kept clean and tight, a good charging system and is never run down or discharged by leaving the lights on, will last a long time. The battery in my car is 8 years old, and even though once the dome light got left on and ran the battery down a bit, it still works fine.
I have seen brand new batteries fail within a week because the buyer installed them in a car that had a faulty charging system.
Most car batteries are not deep cycle - run them all the way down once, twice, thrice and they are most likely done for good and you will need a new battery.
What do I get? It depends, but for a plain old car, I go to Les Schwab and have them install it. They sell decent batteries and stand behind them. If there is a problem, they will not only give you a new one, they will install it.
Most of the batteries most people buy are made by one of a few manufacturers that put different private labels on them. The manufacturers are companies like Exide and Yuasa.
I would not be surprised that Walmart may get something cheap and poor quality - that is their modus operandi; go for the lowest price stuff they can get. For some things they can't get the manufacturer to cut prices or quality so they go with crap.
http://www.fastcompany.com/54763/man-who-said-no-wal-mart