OK, the Hilton Garden Inn is next to Hatton Cross, meaning it is walkable from Hatton Cross Tube station and Hatton Cross bus station. You have to pay to use the Tube and it's very fast, the buses are free, and there are *loads* of them (and you get a free scenic tour of the airport into the bargain ) Big advantage is that it's then very easy to get into central London using the Tube.

HIX T5 is outside the airport perimeter, and so not accessible by free bus. It's on Hoppa route H55 from T5 only. It's also round the corner from public bus route 7 to/from T5 and T2/3, which you have to pay for.

The Ibis is on the Bath Road or the A4, the main 'hotel row' for the original part of the airport. As well as the Hoppas, there's about 5 different free bus routes linking it to T2/3 and T5.