4C engines have the ability to swing larger props, and that's an advantage for certain applications e.g. 3D flight. In terms of reliability, I think 2C and 4C are the same, given that proper operating procedures and maintenance are done. 4C engines require a little more adjustment on the valve gaps, which I do once a year. 4C also requires a little more safety precaution in preventing prop throwing (backfiring) by not overleaning the high end, and using double jam prop nuts. A tach is a must for tuning. Other nice things about a 4C is the "put-put" sound (unlike the high pitch 2C), and less mess to clean up after a day of flying. My ratio of 4C:2C engines is getting larger