I agree with kawoh. I find SK to be nice in Y and C, both. Ex-BKK is naturally cheaper but somehow SK was offering ex-BKK prices for ex-SIN departures earlier this year but you need to purchase tickets in BKK. I don't know if they are still doing this but it might be worth asking agents in BKK. The only problem is that they have only one flight a day and they don't fly every day. SQ is also not bad, of course.

Last year, I once met a guy traveling in UA's F on BKK-NRT, who was heading for SIN via NRT! Leaving BKK at 7 a.m. and arriving in SIN at 11 p.m.