This question pops up periodically and has been addressed and answered countless numbers of times. Please run a seach here and in the Trip report section. There's also an old thread of 800ish posts called 'the Baht Run' which will fill your plate for whatever you might want to know about TG. I think I even did a trip report somewhere in the report section on TG. Just use my handle (
tvl4free) and the words 'snot flight' for what may be an interesting read.
So, yes, the extra $20-25 USD for C over Y is well worth the money! Included on the BKK-HKT route are 747-400's, reclining F
seats4free when paying
just C, and Lounges w pastries, etc.
It's all here! And more! Just search!