Are you going in January? If you are then consider snow, ice and very cold in
Niagara. A couple of years ago it got as low as -99 degrees.

There's not much in Niagara Falls to keep you busy more than about 2 days.... at that time of the year a lot of tourist attractions would be closed, the Maid of the Mist only runs until ?October.
NYC would be a better choice.

-99??? That cant be deg c?

Niagrara Falls, while pretty dont offer much to keep you there for days. I found 4 days there far too much and a night would have sufficed. The falls are nice, pretty etc but the Clifton Hill area around them is horrible, tacky and loud. Lots of haunted houses, tacky shops, fast food places etc. and on weekends the place is swamped by American teens who come over the Rainbow Bridge.

New York would offer far more in terms on variety and things to see and do for a few days. However, depending on how long you are going and budget I would have thought there are far nicer places to go for a birthday trip, both these places will be bitterly cold.

While cold, Torronto is a lovely city to visit, and the best part is the underground PATH system which links many hotels means you dont have to go above ground much, there are thousands of shops underground, places to eat etc and above ground, you got the CN tower to see and lots of nice restaurants. I loved this city.

Alternatively, for a bit of winter sun, the Canary Islands are lovely, not stinking hot, but a moderate temperature.

No reason why you shouldn't do both! We spent a week's holiday in New York, but during the week, we flew to Buffalo for 2 nights at Niagara Falls. Wasn't difficult to do.

But this is in January!

If I were in your shoes, I'd stick with NYC.

You only need a couple of nights in NF. I totally agree Clifton Falls is horrible. Loud, tacky & like Blackpool TBH. However Niagra on the Lake just outside is a lovely little town. Very pretty.

Make sure you have a room with a falls view. We stayed in the Sheraton Fallsview & had a fantastic rom with a huge jacuzzi bath that we could both sit in & see the falls. Maid of the Mist is a must. They do provide rain ponchos but you still get soaked.