I agree that the ys is a quality motor and it's performance is on a higher plane than the os and saito. With it's performance comes some complexity. The original request was for a first time 4 stroke. It has been my observation at our field that first time 4 strokers can become frustrated with setting up and adjusting the ys. It has also been my observation that first time 4 stroker's tend to lean the motors out too much. This is why I recommend low nitro fuel with partial castor oil content. The Saito's like to run rich, the os's will run at a broader needle setting and develop good power with low nitro fuel.

If weight is the primary concern go with Saito. If performance is the primary issue ys is king. For ease of use I would rank the os first and saito second for first time 4 stokers.