Flying in from Europe back to JFK at 9:00 at night. No flights back to MIami, Florida that late. Should I stay over at hotel near JFK, and fly out of JFK the next morning, back to Miami, or taxi to a hotel near Laguardia, and fly out of Laguardia in the morning? My New York friends tell me it's easier to deal with Laguardia.

If you can fly out of JFK, why would you bother with trekking over to LGA? Not to mention the added cost of a taxi. JFK isn't that bad, and you'll have to deal with immigration and customs there anyway.

If you're already arriving at JFK, I don't think it makes any sense to go to Laguardia.

Perhaps your NY friends mean generally-speaking that Laguardia is a smaller easier airport to deal with?

But again if you're already at JFK, yes I would simply overnight at/near the airport and continue on to Miami in the morning.

What your friends likely mean is that LGA is closer to Midtown and easier to reach from most of New York.

Once already at JFK, there is little reason to make the cross-island trek to fly out of LGA.

Are you staying with friends who live close to LGA? In that case go there if it's easier to get to their place.