I would personally go with the 49ers or the Dolphins, leaning towards the Niners. I don't see Andy Dalton being able to match Romo's production against the 49ers D. As for the Fins, the Browns are terrible and could barely score on the Colts D.
I actually like Tennessee. Denver allowed 7 sacks the first two games. Cincy allowed 6. Both teams gave up multiple INTs and FFs. IMO it comes down to which team you feel will score the most points, and I think Denver will score less against Ten than Cincy will score against SF.
Don't get me wrong, SF is certainly a stout defense, and in side by side comparison I think they are the far better D. However, I like Denver's lackluster offense more than I like Cincy's current unpredictably.
I'd go with the Panthers or Dolphins due to their opponents. My only worry with the Panthers is Cam Newton seems to either score or turn the ball over in a hurry, which would give the Jags more opportunities. However, Gabbert's getting thrown to the wolves (still, don't expect a repeat of the Jets game). Miami's defense has been pretty lousy thus far, but they shouldn't give up that much . Actually, screw it. Go with SF (sorry, I'm doing my research as I'm writing this). SF's defense has at least been semi-decent so far and they're playing against a team with limited offensive upside. I like your idea of going with the weekly matchups, but you often end up with weeks like this where everyone has warts where you don't want 'em.