Buy good quality, break them in right, don't run them lean, give them adequate cooling, run them dry at the end of the day, and oil as needed, and either 2 stroke or 4 stroke are going to last a long time. In the end, a 2 stroke will probably last longer simply because it has less moving parts to wear out, but longetivity isn't an issue with the name brands. If you want to run it hard and put it away wet, go with a 2 stroke. If you view engines as investments and do a few little things to protect them, choose based on the application.