I'm equally adept with both systems. But for motorizing bicycles, I think I'd stick with the 2 stroke due to their simplicity, power, and ability to use an expansion chamber for a bolt on power boost. When well maintained you can get respectable life out of one and that by using good oil. (BIA TCW rated or good synthetic after the breakin interval)

As light as a bicycle is the power of a 2 stroke can make it feel like a rocket especially when you get into the power band of the motor where it comes alive.
Wheeeeeeee !!!!