Depends on the airport and airline, but in general I play it fairly conservatively.
out of JFK
- I'll aim for 60 min, with another 15-30 min "slop" in the schedule if I'm going by car (the Van Wyck can be one of the world's truly annoying experiences.)
out of LGA
- 90 min minimum, 2 hours at holidays. If I luck out and get a short curbside check-in line, I'll have a little extra time, but better safe than sorry.
- 60 min is fine.
Any airline in LAS
- 2 hours, only because the security lines can be horrific. I've been lucky last two trips, but again, better safe...
Anywhere else, I'll check the airline's website and go with their recommendation, plus 15 minutes.