I previously stayed at Hilton Terminal 4, which I thought was good. I accidentally made a reservation at the Hilton Terminal 5, and it was a most fortuitous mistake. They have the absolutely best Indian restaurant at which I have ever eaten at the Terminal 5 Hilton. It is called Mr. Todiwala's. If you decide to stay there, make sure you reserve your dining spot in advance.
The day before I ate there, I ate at a Michelin-starred Indian restaurant in London. Mr. T was far superior at a far better price.