Well Mystery machine is a 1960s van, which may add classic-ness points, Hence cooler. The original Turtle Van was probably a modified VW Combi, which is also cool. Cant decide >_<
However the Mystery machine gets points because Its ridden by babes like Daphne and Velma, and hunk Fred of the ladies. Shag and scoob for the munchie induced types.
The Turtle van is ridden by 4 immature pizza eating Teenage turtles and their master sensei who is a rat. Not very classy. Although April O'Neil has her own news van, she is mostly seen riding the Turtle Van which redeems it for babe factor. Still cant decide >.<
on a sidenote the film versions of the Turtle van would destroy the Mystery machine because of its mods. IRL Turtle van vs Mystery machine would probably be a tie because their weapons dont work irl