B.C.
You know LaGuardia and Niagara Falls are on opposite sides of New York state, right?
If you don't want to deal with NYC, then fly into Buffalo and the drive is easy peasy from there.
Or just fly right to Niagara.
Are you doing this in summer or winter?
You couldn't pay me to drive across New York in winter but summer is nice.
Additional:
April can still be a little iffy weather wise - it could go either way - but you'll probably luck out.
(Just once when I was little I can remember wearing a winter coat to watch 4th of July fireworks south of Buffalo but most summers are warmer than that.).