I can't comment too much on US Motors other than most of the OEM pump motors are A.O. Smith if that tells you anything. But usually motors are cheaper for a reason.

However, can I add another option? Because of the spa and in-floor features, have you considered a variable speed pump. This would give you the most flexibility in setting the optimal flow rate for any condition and it may even make your in-floor system work better if you choose to use it. While more expensive up front, the energy saved with this kind of pump will pay for itself over the life of the pump. You can check with your power company to see if they are offering any rebates to help offset the cost. Also, one thing you did not mention was the possiblity of a solar system. If that is added to the equation, then a VS would really benefit you.