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I think most people say it's better to see Niagara Falls from the Canadian side. There are a lot of details though.
In terms of staying in hotels, you're definitely going to have better hotels in Canada, with actual views of the falls from your hotel room. That's pretty cool to see at night too. There's also going to be casinos and other things to do in the area if you stay in Canada.
The American side gives you more of a nature feel, but you probably want to do an excursion on a boat to get drenched under the falls. That's the best way to see everything up close.
You should factor in any delays in border crossing, but for staying overnight, the Canadian side probably gives you nicer views and more options.