I am a QR fan in general, but would have to say that in this instance I would definitely go BA. While on board QR are great, 8 hours at HIA, even with access to Al Mourjan, is horrid, especially as you would arrive around 23h00 and only leave around 07h30 the next morning. The "quiet" room at Al Mourjan is not designed with sleep in mind, so I can only imagine the Business Class lounge offers less chance of sleep. My personal opinion would be head down to LHR, and jump on a non-stop flight. YMMV.