New York

Robert is right about Niagara being far better from the Canadian side. It's quite an awesome sight close up. Worth taking the trip under the falls on the Maid of the Mist boat as long as you don't mind getting a bit damp.

Niagara is very much a one trick pony. Get in, see the falls, get out. The rest of the town is shite. If you need to stay overnight then much better places outside Niagara. If the missus likes cute chinzy little towns in the New England style then Niagara By The Lake is good. It's a short drive from Niagara.