I like Wraiths better then Mutalisks, though. This goes for base tier air units. Although Scouts have the most damage, who in the hell masses Scouts?
No one I know, that's for damn sure. A good fleet of wriahts can take an enemy by suprise if he does not scout ahead and make sure of things, I think. I rememebr Tuna killing me with Wraiths because I forgot to actually use a overlord for detector status. Also, cloaked wraihs are good for sneak attacks, from my experience.
Scourge are okay. To me, they are a fast moving scout, moreso then a Capital Ship Killer. They are both, but generally I use them to scout about rather then nuke some nub masser.