Having been to both sides now...
(Watertown, NY, USA)
The New York side is MUCH better!!!
On the American side, you can park free and easily walk to areas with great views of the falls.
On the Canadian side, while I was researching my trip, it sounded like there was free parking right across the street from the visitor center, just like on the American side. When I actually drove to the Canadian side however, I found that the only parking lots near the visitor center were paid. In Canadian, they were about 20 each. You could park a long way away (five miles?, seemed like) for a flat fee of 10 Canadian.
But there was another problem. Even if I wanted to spend lots of money AND TIME waiting for a bus to backtrack several miles...the falls viewing area on the Canadian side was absolutely packed. There'd be no way a family could possibly enjoy being crammed in toe-to-toe with hundreds of thousands (estimated) people like that.
On the American side, there were lots of people also. But the density was a lot lower. It felt more like a typical tourist destination, rather than the total chaos of the Canadian side.
And, from what I could see...the view is just as good on the American side.
What's missing from the American side is all the cheesy tourist traps. If nothing else, that reason ALONE makes me feel foolish that I ever chose to go to the Canadian side.
The American side is better. MUCH better. Now that I've seen both sides, I'll be taking my family back (when the kids are older) to the American side...and I won't bother trying to cross the border at all, except for riding Maid of the Mist.