Hi Christine, welcome to IIS
I'd like to build in place that had good clear skies for most of the year, good transparency and little to no skyglow from town/city lights. Hill or flat wouldn't worry me, although I'd prefer the hill situation. Just feels right and that's where the professionals like to build...and you want it to look professional
Not only that, but a good view from your home, when taken advantage of, will make your house and property worth more than otherwise
. Plus, having a nice observatory with a large dome sitting on a hill/ridge in sight of your house just looks dramatic...and would be a conversation topic, for sure