Hmm I seem to have opened some lively debate. Just to clarify the original question that I had posted was based upon the Trad Plus 8 and not any new versions or one off's, although both the "Aero" plus 8 and the "le Mans" plus 8's are quite stunning.
I was thinking more along the lines of whiche period, derivative, colour combo and upgrades would make the most desireable Plus 8. All subjective of course but it would be interesting to see what trends emerge.
From the initial responses, it sounds like the early narrow bodied cars have the edge. Not my cup of tea as I prefer the later injection cars but i can see the simplistic, original beauty in them.