I stayed at the Miller Villa and at the Astor at different points during my stay in Shanghai. They were both beautiful historic hotels, and so will attract a fairly similar type of traveler.
Overall, the Miller Villa was more polished than the Astor in terms of both service and room quality. Both a worth a stay, but all else equal, I would probably choose the Moller Villa (but could see the case for the Astor House, too - Bund location, more historical feeling standard rooms, and a jaw-dropping breakfast room.)
The service was pretty medicre. For example, I wanted to check out 2.5 hours late, and they refused to do so without me paying half of the normal room rate. I could tolerate some kind of fee; however, half was ridiculous, especially when the maids cannot possiblely clean all of the rooms right at noon. Otherwise, the service varied from helpful (taxi cards to the correct destination) to disengaged (I.e., taxi cards to the wrong destination)
That said, the hotel was memorably beautiful. And patchy service is not uncommon in China is not uncommon for hotels in this price range. I stayed at a third hotel in this same price range (the SSAW / Narida South Bund) and it’s service, for the same price, was much more helpful. I also preferred its location and breakfast offerings. But it did not offer historical flair. So each of the three hotels I stayed in was memorable for different reasons.