I am partial to YS engines as they have the most OOMPH in their class. However, YS engines can be more complex as they have a pressurized and regulated fuel system. This allows the fuel tank to be placed anywhere in the airframe -- on the CG is best as you get no CG shift with fuel burn. Saitos are less complicated and often times lighter than a comparably size YS engine. Saito engines are also known as great running and reliable engines. The already mentioned OS .91 is another highly respected and reliable engine in this size range.

As I have said I love my YS engines, but your future Stuka won't need the most OOMPH you can buy. An OS 91, a Saito 91 or a Saito 100 will fly it very well. A YS 91 will also fly it very well, but I think the 1.10 is too much. Heck -- a strong 61 2C will fly a GP Stuka pretty well...

My advice is to get what you like and what you can get the most local help with. Being the first one with a new and balky engine at your field can be very frustrating...