the first black ops hands down had the best. i really enjoyed call of the dead and five and could play those two maps for hours without getting tired. ascension and shang ri la were also fun maps because they were more challenging
Love my some WaW zombies, but I'd say my favorite has to be BO2 just due to the differences between the maps. It's something I don't get tired of as quickly as most of the newer ones such as WW2, BO3, AW, etc.