Start with the manufacturers recommended plug. If it runs poorly, try altering the heat range up or down. I run OS A3s in both my OS LA 46 and my Thunder Tiger Pro 46, and an OS #8 in my Thunder Tiger GP 61. Asking which plug is best is like asking if you prefer Blondes, Brunettes, or Red Heads. Everybody has a different opinion based on their personal experience. When you find the combination that works for you (reliable idle, good transition, high top end with an engine properly tuned), stick with it unless you find a reason to change.

Brad