I have shopped in both, but prefer Target. The Target is cleaner, further from my house, so I shop Walmart more.
A long time ago I read the unauthorized biography of Sam Walton (good book), and he wanted the isles wide enough for customers to get around, but his advisers said that he was losing money with empty space. Two months after I read the book Sam Walton died (I was inside a store when they announced it), and two days later they had racks with product in the isles.
Interesting thing about Sam Walton was he had a pilots license (and would I assume his own plane too), would fly around, and do surprise visits to his stores. He fired one manager when he walked into a store, found something wrong that needed to be fixed, pointed it out to a manager to fix it. The manager told him "yeah sure, who do you think you are; Sam Walton".