I just spent two summer months hopping around Europe's nicest points hotels. Here are some of the Hilton (affiliated) ones.

My number one answer would be Canaves Oia Suites. If you can request villa 31, it'll be even better from a privacy perspective. The property and views are indescribably beautiful, and there's nothing like waking up early enough to watch the moon sparkle over the caldera before giving way to one of the more beautiful l sunrises you've ever seen. I also spent some time at Canaves Epitome for its proximity to Ammoudi Bay but, in my opinion, Suites is the true essence of why you go to Santorini.

Next would be Grand Hotel Victoria Menaggio. Incredible hotel, right on the lake, and with the best spa you'll ever see in a hotel. There are also reasonably priced classic wooden boats that will take you on a tour of the lake. There are few more romantic things I've experienced than skimming across the lake in a gorgeous private boat, James Bond style, with your partner and stopping to take a refreshing dip around many spots. Also it's pretty easy to ask them to let you out at Villa Balbionello so you can explore the ridiculous views from there.

Hilton Imperial Dubrovnik is also super underrated. If you get upgraded to a suite, it's a fantastic view right into Old Town, but enough steps away to escape the crowds and heat. Dubrovnik itself is drop dead gorgeous. If you like to swim, there are bars within the walls of Old Town that also have cliff jumping spots. You can easily spend a great afternoon at one of them.

But mind you these hotels I mentioned tend to close in the off season so I'd double check before making final plans