whichever is the best car and the right price!
It wouldn't bother me either way and I would say to anyone else the same thing.
both have certain pro's and cons,
but generally go for the best maintained and mechanically sound car with good history.
Dealer sale you will have come back if you have problems, private is pretty much sold as seen.
Dealers tend to be more expensive becasue of this peace of mind they offer plus they are often in no rush, where as private sales tend to be cheaper because of the opposite of above.
etc etc etc................
