Throughout your life you develop gold standards. For me, the best mountains are the Alps, the best decade was the 70s, the best birthday cake is tarta baba with lots of lemon glaze, and the best falls are definitely Niagara.
It was 25 years ago that I first saw Niagara Falls. I was on the kind of wonderful road trip you take when you're relatively young-- it lasted weeks, and we went from Washington DC to Hamilton NY to Ann Arbor MI to Hustisford WI. In addition to the thousand and a half miles of North America we traversed, there was a wedding, a reunion of college buddies, and an island cottage along the way, but it all paled in comparison to Niagara Falls. The roar and the spray and the prisms of light stayed with me long after I returned home.
Since then I have had the good fortune to visit Niagara a half dozen times or more and they never disappoint. It doesn't matter if there's a crowd or that the water flowing over them is less than half its natural capacity, and never mind that the honeymoon thing is sort of baffling; I am even able to disregard the tacky merchandising that inevitably goes along with any stop there, because the falls themselves