Recently I did quite a bit of investigating 4 stroke engines. The result of all my investigation was in favor of Saito. This was for several reasons. First of all, they make only 4 stroke engines. It is there sole business. Second, I like to design as well as fly. There have been times where I wish I had used a bigger engine. Saito solved that issue by making many sizes in the same case and mounting holes. The 65, 80 and 91 are the same case. The 72 and 82 are in another case. Last but not least, the 120, 150 and 180 are in yet another case. So if you are having questions as to which engine for what plane, you might find a group you can live with. Also if you are looking for some real good information on Saito, go to this site:
http://saito-engines.info/