They are both fine. I wouldn't say "I'm good about mathmatics," however. It just sounds strange. And to me, "I've been very good with being quiet" sounds odd as well.
I may just be a regional thing, but if I were to say "I'm good with being quiet" it would mean I have no objection to being quiet. If I'm good with taking the dog out every day, I have no objection to it. If I'm good about taking the dog out every day, I actually do it. Again, it may just be a regional thing. The grammer gods will have to give you the actual rules.