I think it would depend on whether you are going by yourself or you have a passenger.
Another factor would be the amount of stuff you want to carry with you. Some bikers
will carry camping gear, others will stay in motels or with friends along the way.
The other would be the amount of maintenance you are willing to do on your own. Newer
bikes are more expensive to buy, not to mention limited upkeep that can be done on their
own. Older bikes, although cheaper to purchase and can be worked on based on the bike
and the skill of the owner, don't always have the same availability of parts or accessories.
Also you have where you live as well. Europe and Canada tend to favor the BMWs while
over here it's the Goldwings and Harley Davidsons.
If I was riding by myself, I would ride my 1983 Silverwing due to the reliability and,
well, I already own one. If I was to ride a long distance with my wife, I would look
into a 1985 Goldwing with the fuel injection. Also would have more room for what I would
take along for the trip.