I am flying SIN-LHR with my wife early Sep on vacation in D class. Both of us are LH Senators, and are sitting on standby upgrade vouchers for UK *Gs. Any suggestions on the best route to maximise probability of getting upgraded- SIN-FRA-LHR with LH or SIN-BKK-LHR with TG? I know SQ business would be almost as good as LH First- but since we are sitting on this freebie vouchers, it is a good opportunity to use them and save a few hundred pounds (since LH and TG are a bit cheaper than SQ and we are on vacation). Any suggestions?