Take the words "hovers at half throttle" with a grain of salt. Throttles are NOT linear on R/C airplane engines. When the throttle stick is halfway between idle and full, the engine is running at closer to 3/4 throttle. This is why the YS hovers at "half throttle" but barely pulls out at full throttle.

Help I am tired of all these conflicting opinions, please someone what is the best motor for this plane?

Welcome to the real world, and R/C aircraft. Everyone's experiences, and perceptions are different, and that doesn't even take into account environmental differences such as atmospheric conditions or manufacturing variations in engine and airframe. If you end up with an unusually light airframe and/or an unusually strong engine, the plane may be absolutely amazing. However, if the materials coming down the assembly line happen to be on the heavy side and/or the engine is a bit tired, the airplane may be a total dog. In other words, it's the luck of the draw.

There is no One True Best Motor(tm) for the UCD3D, as there is no One True Best Motor(tm) for any airplane.

I know all you need is one more opinion, but I would probably go with the YS91.