JFK and LaGuardia are 20 minutes away from each other, it makes no difference. JFK might have more traffic driving out of it, but distance wise its the same thing. LaGuardia looks like its alot closer on the maps but I live in queens and it takes me probably only 15 minutes longer to drive to JFK than it does for me to drive to LaGuardia, and if you want to get some idea of relevance, I live near the 71st Avenue - Continental subway stop in Queens on the F, E, V, G, R subway lines (the green/yellow/orange and blue lines that run along side each other in queens. See subway map below).
now, Newark, on the other hand, is like two hours away, so i'd stay away from Newark. Unless you really like smelly parts of NJ.
Oh, and FYI.....all taxi cabs (yellow cabs only) have a flat rate from airports to Manhattan of, I believe, 40-45 dollars plus tip. Einstein is in the Bronx, so, you can either cab it into manhattan and take the subway up to the bronx, or just suck it up and pay an extra 20-30 bucks and save yourself the stress of dragging all your crap all over the subway and just cab it to the bronx. You're already spending all this money flying in and applying, whats an extra 30 bucks on the cabfare to get a ride to the Bronx? let me tell you now, the subway isnt bad, but coming from the airport there is no direct train. You'll have to transfer several times, and it is a huge pain in the butt.
As a lifelong resident of NYC, who works in manhattan and lives five minutes from both JFK and LaGuardia airports...save yourself the stress and if you can afford a little extra, take a cab on your way to the interview. Then, if you really want, on your way BACK from the interview you can deal with the hassle of the subway to save money going back, but relax on yoru way to the interview. The last thing you want is to show up sweaty and tired, having spent two hours transfering subway and/or bus lines to get from queens alllllll the way up into the Bronx. In case you have no idea how far it is from queens to the bronx by subway, go look at a subway map.
http://www.mta.info/nyct/maps/submap.htm
OH YEAH, I ALMOST FORGOT- there is an airport shuttle too. There are several , actually. Any airport to manhattan for as little as 13 dollars. Way better than the subway. Here's one:
http://www.goairlinkshuttle.com/page.php?page_code=RIGHT1
There are no direct trains from queens, let alone the airports, into the Bronx. See all the different coloured lines? You have to transfer every time you change "colors", and sometimes they come on time, and sometimes you get to wait on the sweaty, hot, no air conditioning platform. And if you are lucky enough to arrive in rush hour, good luck, yo'll be crammed into the car like a sardine. Which is fine when youre used to the daily commute, but if youre trying to relax before your interview, i wouldnt reccomend it.
cheers