If Terminal 3 and a fellow Hilton whore, you need to consider the Doubletree on Bath Road, plenty of TfL buses shuttle between the Doubletree and the Central Bus station, it's 2 stops after the free zone, so you need an Oyster or contactless debit or credit card. Often very good rates there, and breakfast is better than HGI. There's not much hassle differential between HGI, Hilton T4 and the Doubletree, the bus at least goes to almost the door of the Doubletree and the other involve a hike from their respective stations.