I had to look up Hair Metal to see what you even meant by it. Some of it is garbage. But Guns n Roses certainly was not. Bon Jovi was solid. I tended to like the ballads all right among the others (Every Rose Has its Thorn). I think of most of it as "strip club music". Twisted Sister had one of the best videos of all time. Have to give them credit for that. The Hair bands were mostly a 90's thing anyway.
As for the worst of the 80's. George Michael, New Kids, Michael Jackson, Hall & Oates and the aforementioned Christopher Cross. Honorable mention to Madonna, Paula Abdul and a host of others.