I live in Bristol (most of the time) and almost never fly from the airport, unless to take a cheap KLM ticket to AMS to take a cheap BA EX EU fare to somewhere far.

I always normally book from LHR and then book a national express bus to heathrow, most of the time it does the trip in under 2 hours, always reliable and costs anything from 1.50GBP one way, which is insane for cheaper London fares. Yes its a bus, but its just fine.

Personally I find BRS airport only good if you want to take a leisure flight somewhere on easyjet, TUI, Thomas Cook or Ryanair.