I use either Thai or EVA, but mainly EVA for the last 4 years. I'll explain why.
Living in Bristol, Heathrow is our best Airport to fly from. We could fly from Bristol to Amsterdam and then connect, but did it once with China Air and it was, to be honest, a friggin nightmare.
Heathrow is 2 hours from home, so easy to get to.
I like the THAI and EVA Flight times, 9pm ish. This means I can get a half days work done, then leave at 4pm to get to Heathrow.
I don't samoke or like a break to stretch my legs, so direct is perfect.
I like to arrive in BKK around 3pm as connecting flight to Udon is c5.15