Tough one, but SF might be leading the league in turnovers, so Chiefs are an attractive play. However, SF's offense dropped 417 on the Siants and if last week is a sign of things to come, they may become a very potent offense (and undoubtedly will be very careful with turnovers after last week.) It's possible that SF continues to hurt itself though, especially in a hostile environment.
The Phins are also attractive because I think the Jets offense will remain inconsistent. Miami is also a solid unit anyway and can force turnovers. Vontae Davis might be a top 5 CB come the end of the season.
I think the law of averages will favor SF this week (ie, cleaner game), so I think the safer play would be the Fish. Even if the Jets play well, they rarely account for a lot of yards.