I greatly prefer quill bodied flies though I don't use them exclusively. They are prettier (to me - not sure if the fish think that too) and I think I fish them with more confidence. I'll often tie my Adams' with a grey quill body rather than the standard muskrat dubbing. On several occasions I've fished the same area of a stream with both the dubbed and quill bodied Adams and it didn't seem to make any difference whatsoever to the fish. I ended up catching about the same size and number of trout on both styles of fly. For some reason my quill bodied flies tend to look just a little more "buggy" to me and I'm able to achieve a really fine, tapered body and...well they just "look right" to me.
That being said though, one of my absolute favorite patterns is the Parachute Hare's Ear, which obviously does not use a quill body. So I guess I like both styles of fly (and biot bodied ones too).
-Darryl
My one wish is that when I die my wife doesn't sell my fishing stuff for what I told her I paid for it...