JFK to Grand Central will be a bit of a pain (at least until the LIRR East Side Access opens some time this year!). AirTrain to E subway train to 74th/Roosevelt to 7 train to Grand Central. Or taxi/car service for more $$ and probably only modest time savings depending on time of day & traffic.

But I think a connection into either LGA or HPN would still take more time overall (no LAX-LGA nonstops either).