The 1965 GTO convertible is the most usable classic GTO and the one I recommend for someone who wants to actually drive their muscle car regularly.

The convertible body adds flex to the unibody that the hardtop doesn't have, which means the ride is slightly less controlled. But the experience of driving a 389 Tri-Power GTO with the top down on a September morning is not something any hardtop replicates.

The 1965 model specifically: the tripower was still available, the body style was in its second year and all the first-year issues were addressed, and the convertible bracing was improved over the 1964. The 1966 is similar but the 1965 has the slightly purer original design.