Parking Orbits for Comets and Asteroids

Is it the Oort outer belt (outside of Pluto) or the Kuiper belt? What
gave comets their great elliptical orbits. I would think a round orbit
was closer to the reality of gravity.Seems to me comets should in time
line up with the surface of the sun and hit. We watch Jupiter being hit
by a comet.(famous pictures) I really don't see much difference than a
comet or an asteroid,but I'll bet on a comet that hit the Earth 130
million years ago as being the one that wiped out most of the cold
blooded animals,and made room for us mammals. Bert