Hi Tom - T5 is a vast improvement on the squalid earlier Heathrow terminals. The cavernous height, lots of natural light and general sense of spaciousness is a welcome change to the rest of Heathrow. So, as far as passing through Heathrow goes, T5 is definitely the best terminal.

However, as earlier posts here indicate, there is something sadly lacking compared to most flagship international aviation terminals. The fact BAA seems to think of itself first and foremost as a retailer, and secondly as an airport terminal operator, is reflected in the layout of the building, and the circuitous routes through which passengers are more of less forced.

It doesn't seem to be designed for either efficiency or comfort, but as a shopping mall with airline gates attached.