My pick for their worst single is Angel, which was a hit, or Fly Away From Here, which was a single from Just Push Play that was unsuccessful. I think their worst song is Otta Your Head, which is not famous but I think you've listened to it because I've posted it before in discussions about what the worst Aerosmith song is.
Flesh vs. I Don't Wanna Miss a Thing...I think Flesh is a less competent example of songwriting, and both songs exemplify something that went wrong with the band in the '90s, but I think Flesh by itself is pretty harmless. It's band but if the rest of the album was better then it would just be a bad song that I skip. If the rest of their '90s career was better I would probably dislike I Don't Wanna Miss A Thing even more.