For me it's a combination of which airport to avoid - LHR or DXB and whether or not you like 10hr + flights... nothing to do with the aircraft. Most people would struggle to tell the difference between an A380 cabin and a 777 cabin. I'd quite happily spend an extra couple of hours in the air for the benefit of avoiding the zoo of LHR. And when travelling economy, 6-8 hour hops are vastly preferable to those 10hr, 2 meal, 5 movie marathons. Transit in DXB is not a problem provided you have a reasonable connection (2hrs min / 3hrs max). Cabin service on Thai is better and Inflight Entertainment on Emirates is better. How much value you place on plastic food on plastic plates served with plastic smiles only you can answer. As for the aircraft itself... sure the A380 is quieter than the 777 but it's not so great in turbulence.
An important factor for me is the choice of seat - forward on an aisle away from the toilets... Bulkhead on the bog is the worst seat on the plane.
By far the most important factor for me is the price. No way I'd pay more than £200 more to fly Thai. I can buy a few nights in a decent hotel in Thailand for that price.
MAN - BKK : if it's slightly cheaper, I'd go Emirates. If it's the same price I'd go Emirates. I live in Scotland and travel to SE Asia several times a year have done so for many years. I prefer to travel several hours to GLA in order to avoid London or route through AMS. Having been a regular traveller through LHR and LGW through a lifetime of work, I now avoid those airports like the plague.