I am building one now, and I have allocated a lovely YS 91 to it.

A friend at the field flies his with a Saito 100, and to be honest either would be a good choice, but I am of the bigger is better school of thought.

WHy a YS 91, if you have to ask then you don't have a YS 91, it is a great engine,

So there you go, a great plane + a great engine = lots of fun

All of the choices given in this thread would do the job, IMO

Steve