Having travelled in both, I'd pick TG over SQ for seat pitch (not counting exit rows of course) and food; SQ over TG for IFE and service.
I could be wrong (check over on the TG forum), but the TG flights from Scandinavia (CPH, ARN?) to BKK have the premium economy service - ie. the old business class is sold as premium eco while the old first class sold as business. Just something you might want to consider.
Also depending on how often you fly, if you make TG ROP Gold, you get a roundtrip upgrade voucher which you could use all the way from Europe to Oz. Also, you get one more of these upgrade vouchers to use in your birthday month (+/- 1 month).
I'd say for a medium to long-term strategy: fly SQ, credit your miles to TG till you make *G, then switch to flying TG for the upgraded flights.