It's your choice!

Please note that just taking a subway train will cost you $1.50 each way pp!

Some possibly useful links:

http://www.nyairportservice.com/

http://www.panynj.gov/aviation/jfkframe.HTM

http://www.limos.com/

http://www.citidex.com/20.htm#C4492

Taxi's typically cost you about $40-45.

The Carey Bus to Grand Central and/or Port Authority Bus Terminal costs about $15, and yet there are other options that will get you to a drop at various notable hotels and/or other places for approximately $15 or so (tip for the driver NOT included).

Some use an Olympia bus and even report they like it!

Allstate, Carmel and Tel Aviv are among the must recommended and also maligned car/limo services mentioned on FT in the past!

FWIW, Boston Coach has a rep as being very high cost.

Personally, I'd just grab a cab when I arrived! Hope this helps. Enjoy your trip!