One thing to keep in mind, almost all of these engines use the same basic carb/brand (Walbro). So, unlike in years past with glow engines, the quality of the carb made a big impact on choosing an engine. One of the reasons O.S. max was so popular. Their carbs were always easy to set and reliable.

Now with the gas engines getting more popular, I think it is important to see what is popular, and who is having success. Then, find the configuration to suit the plane you are building. If I were building a twin, I would use mag engines, as I find them a little more reliable. This is because there is one less system to fail. The batteries and switches associated with the EI. This is my opinion though.