To chip in I would prefer TG in Economy rather than SQ. In particular if flying in Oct (still low season to Thailand) there is a good chance of an empty seat next to you. Seats also feel less cramped with TG IMO.
The BR lounge at BKK is very nice - much nicer than the Kris Flyer lounge at SIN for Star Alliance Gold. I have yet to try the new TK lounge at BKK. So I would vote for TG via BKK.