"... if you get caught between the moon and New York City... the best that you can do is fall in love..."
Christopher Cross (yeah, I'm old)
Going somewhere you've been before, if it was an especially good time, is a good place to propose.
However, if you're looking for somewhere new and different, you could go where countless lovers have gone before: Niagara Falls. Yeah, it's cheesy, but it's beautiful. You could also try a cabin in the mountains or a Bed and Breakfast on the New England coastline. California's wine country would also be romantic.
Best wishes.