Wow, Eric. That's the loaded question of the day!!! Vicky answered so eloquently. Hotter to sit on? Vinyl, hands down. Hotter - heat energy - cabin temperature? Proabably the same. Vinyl does not keep heat energy as long as leather, generally speaking. Personally, if I were not locked into the "all original - low VIN" thing, I would pay the big bucks and have the interior done in leather like it was originally intended and the way cars should be upholstered. Leather - black leather - is a bear to keep from drying out. Leather is serious high maintenance. Vinyl lasts much longer. It is much easier to keep clean. But I'm sure Vicky would agree with me on this. There is nothing as nice as leather.