Having flown both of them in the A330/340 my feeling is that there is not enough difference in the hard product to motivate choosing one over the other. The Senator lounges are clearly superior to the CPH lounge, and I do find the A380 in Y to be quieter and more comfortable than the A330/340, but I have not yet tried it in Y+. With those factors in mind, for me it would come down to getting the best routing, timing, and price for the trip in question.