The mnain advantage of Qimage is the finer separation of nearby tones, i.e. distant foliage that frequently turns into undifferentiated mush from PS. Additionally Qimage resolves somewhat finer details and seems to give slightly better microcontrast. Granted som of these differences can be subtle, but I've studied enough side by side prints to confirm the improvement to my own satisfaction. Printer is the Epson Stylus Pro 7900.
Having said that, I haven't printed from the very last iterations of LR/PS, perhaps there has been some improvement to their printing engine. I haven't seen any such claims though.