Not necessarily the most beautiful, but the most flawless. It has to be good looking sure, but more than that it has to not have a single off-key in its symphony of design.
I reckon a lot of people would suggest the E-Type, but I'm not convinced. The windscreen is a little too vertical to be a smoothly flowing design, and the tail-lights don't quite look perfect sitting on top (S1) or below (S2 & 3) the bumper.
I don't think these details are detrimental, in fact the windscreen is part of the charm of the E-Type's design, but they are nonetheless tiny little flaws.
Personally, I'd nominate the Fulvia. It's such an achingly pretty little thing, and I can't find a single sour note in the whole design.
Not only that, but it's mechanically beautiful too, with it's little clockwork gem of a V4 and FWD when FWD was still something special.