The motor that will last the longest is the one that is best taken care of. It's impossible to say what motor will last xxx,xxx miles or determine which is the best in terms of longevity. There are a vast number of variables that determine the life of a motor.

Shop around for the best maintained car and keep up with the maintence yourself and you'll be golden. The car with 230k mile motor that's been well maintained could easily last you far longer than the 105k mile motor that's been abused and neglected.