It's far and away the most convenient as far as access goes--Amtrak goes right to the (free) (maybe not see below) AirTrain which is like a 5 minute ride to the terminal.

But... It's EWR. It's earned a reputation as one of the worst airports in the country. Almost 1 in 3 flights are delayed, and they've got the longest average delay in the nation. Meanwhile, despite or maybe because of how accessible it is the terminals are very small; I don't think I've ever been there when it wasn't packed to the gills (except for red-eyes in when nobody is at the airport at all). I still fly out of there, since it really is the cheapest and easiest to get to of all the major airports, but it will have its downsides too.