I would say that either the Saito 100 or 125 would be great choices. I'd probably decide between these two based on how much money I could spend, and how much power I felt like I needed. (Too much power is ALMOST enough!) The 125 is $60 more than the 1.00.

I know of a couple Magnum 4S engines out at my flying field that have been problematic for their owners this past year, but I don't remember EVER seeing a new Saito with an issue that couldn't be resolved with better tuning and/or adjusting the valve clearances. Since I haven't actually worked on those Magnums personally, it is possible that they just had tuning issues too. (I actually tried to volunteer to help the Magnum owners. However, in both cases, it seemed like my help wasn't really appreciated, so I didn't push it. They never did get them running well, and one lost his plane due to a dead stick just after take-off.)

I don't think that a YS is the best choice for a 1st 4S. They do have extreme power, but extreme power comes with a price! If nothing else, just the extra cost for high nitro %.

I have just been SO happy with my Saitos, it is tough for me to recommend any other brand of 4S. I really like my OS 4S engines too, but they just don't seem to have as much power to weight as the Saitos.

I would probably buy another Saito if I were in the market for another 4S right now, and that is why I recommend them to you.