Been there over 20 times with every direct airline, and some indirect, which I really wouldn't recommend. The best overall IMHO is the Thai daytime flight, TG916 from memory. On the last 2 occasions, when I've flown this flight, I've had 4 seats to myself. On both occasions the flight was two-thirds empty. The night time flight always seems full. The other benefit of the day time flight is that you get into BKK just after 6.00am, so you've got a full day to have a kip, and then find something to do in the afternoon. Have fun !!