Walmart. No contest. Horrible employees, mostly annoying customers, the store is messy, carts are beat to hell/loud/non-straight-tracking, the aisles are often too tight, they are almost always out of about 1/3 of what I went there to get, the quality of most of what they sell is low, the checkouts are all closed and the few that are ever open are as slow as molasses. At least they don't do stupid loyalty card crap and don't blast music.
Target is the exact opposite. Very nice employees, mostly quiet customers, clean and bright and organized, rarely out of anything, aisles are wider, quiet and non-broken carts, checkouts are always fast, higher quality average products. Prices are higher and nowhere near the selection for food as Walmart, but it is worth it. I would gladly spend the extra if I could get everything I needed... but, alas, I don't have much choice but to visit Walmart. So I try to go as rarely as possible.