I would say definately get the limo bus. Depending on traffic door to door it will probably take a similar amount of time as connecting trains and associated confusion. I took this bus in Nov to the Hilton. It was around 10.30 and the traffic didn't hold us up at all. The trains are great and easy to use once you get used to them but after a long flight there is nothing more welcome than a bus that takes you right to the hotel door.

Do not under any circumstances take a taxi (unless you want to pay more than the cost of your flight!!)