Heathrow Hilton is OK at best. Several stays (as a Diamond) yeild little in the way of upgrades or amenities. I've pretty much given up on that hotel, and use Paddington instead. Heathrow Express gets you to the terminals almost as fast as you can walk from the Heathrow Hilton. Only 25 pounds round trip. Depending on what airline you are arriving on, it could be quicker to go into Paddington than take the Express to terminal 4 (which is the only way to get over to terminal 4) and then walk to the Hilton.