I went through this a few months ago buying the engine for my 33% Extra 330L.

First off, both are great engines, and great customer service.

The BME is lighter, and will fit in smaller cowls like the Extra without cutting holes for the spark plug caps.

The DA will fit within the Cap's wider cowl.

The DA has more torque, and the additional weight helps balance the H9 airframes that were designed for the heavier Zenoah engines.

For my plane, I went with the DA, even that it meant cutting more holes. If I were building a plane that had a lighter tail, then the BME would have been chosen.