Here's my two cents on what you've done so far:
Giants: Update is perfect.
Miami: Nothing too crazy, but overall is a solid look.
Buffalo: A for effort on the helmet, but I just don't think it works. Everything else is on point, but too many pants options, and blue should be the primary pants for the away.
NE: The stars & stripes things is a little too collegiate, and dare I say tacky for my taste. But I do approve of the removal of silver.
Jets: The modernization is something I really think they need to do. Their look is quite stale in my opinion, and the new logo looks great. Only thing I would say is it needs shrunk a smidge, and I'd put a white stroke around the box that "New York" is in, so it "punches out" from the rest of the logo. Matter of fact, I'd probably do it to the jet as well to separate it from the border.
Bengals: Update is alright. Not anything too fancy, but I do look the removal of the drop shadow outline on the numbers.
Steelers: As a life-long Steelers fan, I have to say that I'm completely against this concept. There's hardly any remnant of the 5x Superbowl winning uniforms, and gray on white/yellow is anything but legible. I'd say to go back to the drawing board on this one.