If you look at the definition of "good" in Noah Webster's American Dictionary of the English Language, it will say "fit for a particular purpose" to say that nothing is any better than anything else is to ignore purposes.

No higher-rank types in Scala, I'm afraid.

As for the monoid instance:

def pairMonoid[A,B](a:Monoid[A],b:Monoid[B]) = new Monoid[(A, B)] { def empty = (a.empty, b.empty) ... }