Once of the best value hotels at Heathrow, especially for a weekend stay, is the Holiday Inn Ariel on the Bath Road at Harlington Corner.
The circular hotel is about 10 minutes on a regular bus and it is (just) in the free Heathrow Travel Area.
The hotel is usually busy and seems to only allocate rooms to Platinum members of Priority Club at check-in. Most other hotels I use allocate rooms in advance. This means that quite often I miss out on upgrades here. The upgrade is to an Executive Room, which is typically larger, has a bathrobe, water and bar of chocolate in the room.
Check-in found me such a room and asked whether I wanted a drink/snack or 500 points. I took the points.
The room, facing the end of the runway and the main road was not noisy as they have effective silencing of noise from the windows. The bed is a standard Holiday Inn offering, not that comfortable for me, but fine for one night.
Hard and soft pillows were offered.
An affordable room, with a restaurant on site, and in the free travel zone so you can avoid the Hotel Hoppa fares. Don’t expect luxury but it’s clean.