I live considerably North of NYC and tend to avoid it like the plague since I moved. But I'll let you know.
As for which airport... Well, LGA has a more funner approach, in my opinion. Some prefer the word "harrowing," especially the base and final to 31. I know people who will not, under any circumstances, fly into LGA. But I rather enjoy it. The approach is much more scenic and somewhat less odorous than flying over the refineries and chemical plants in Jersey. In bad WX, there's also the thrill of wondering whether you'll be on dry land when you depart the airplane. It can be exhilarating.
LGA also has the shortest trip to Javits by taxi -- assuming that there's no traffic. If there is, all bets are off. When I say it can take anywhere between 20 minutes and two hours to get from LGA to Midtown, I'm not kidding.
You can also take one of several buses from LGA to various train stations where you can catch the 7 train, which will leave you practically on the Javits Center's doorstep now that its been extended. The 7 line, that is, not the doorstep. That's probably how I would go. It should take maybe half an hour to 45 minutes total.
On the down side, LGA itself is a dump. Seriously. It's old, dingy, dirty, dreary, and depressing. Departure security and check-in time are probably the worst of any airport I've ever used. I've spent hours on line there. It got to the point that when I used to have to depart New York during peak hours, I would drive to HPN -- and I lived 10 minutes from LGA.
As for EWR, I haven't made that trip in a very long time. I do know that there is bus service from EWR to Newark Penn Station, from whence trains can be taken to Manhattan. There are also buses that go directly to The City. It's been a long time, but I remember the buses being about an hour ride from EWR to Midtown. Improvements may (or may not) have been made since then. I think there's an AirTrain now, as well.
Rich