I have both. I was a two stroke guy for 15 years. I still think they have there place. That being said a 4-stroke is less trouble than a 2-stroke. Less trouble= fewer dead sticks and less turning the needles. The valves do have to be set a few times a year. It's a 5-10 minute job. I have four Saitos. I started with a 72. I had to tune it with a tach until I got used to the sound. Now I can tune one by ear. However I rarely tune it. During the summer I never touch the needles. This time of year when the weather cools there is some temperature related adjustments. It seems like I tune my two strokes several times a day.
I mentioned Saito because that is what I have. OS and YS also make fine engines. I just would not suggest the YS for a first time 4-stroke user. Once they are set they are fine. They just seam to be a litle harder to set. If someone you fly with runs them then you would be fine. No body in our club runs one and help is 100 miles away for me. So I don't own one.

David