I am more or less a lurker at both sites. I think Ironraven summed it up perfectly, especially this: "Not as refined, and the fringe is a little more likely to stumble in...". Zombie Squad is WAY more likely to attract the ,<censored> and its posters are not generally as respectful as ETS. If you have questions about ZS Chapters I would shoot an e-mail to one of the mods over at ZS, the guy in charge is named Kyle, though they are all pretty helpful.