It depends on how adept you are with engines. If you are not to power hungry, The OS is a no brainer. Very user friendly and will run all day on 10% fuel and should give similar performance if propped correctly. A saito 180 with a Kline regulator will give you much better performance at the cost of slightley higher vibration, higher purchase cost and lower fuel milage due to a larger displacement. It may also be slightly more difficult to break in and tune. Unless you are an experienced 4 stroke operator, I would wait on the YS. The question you should really ask yourself: Where do you plan to end up in the hobby so you can buy the engine you are more likely to need down the road. Think ahead and save yourself some money down the road.