Oia is known for having the best sunset in Santorini but it isn't hidden. During peak tourist season the village fills up with people anticipating sunset. However, you can find spots in Oia that aren't as busy. For example, if you are staying in a villa overlooking the water, you might be able to have a spectacular view without leaving your outdoor patio! It's worth it to take the extra step of booking a sunset-facing room so that you don't need to go very far to see a nice sunset.
As said above, Oia is the most famous location for the sunset. However, since you are on a island, you can catch the famous sunset from various locations, just facing west. You can also book one of the several sunset cruises that are organised during summer (April to November) and most of them set anchor below Oia to admire the sunset avoiding crowds.