I've flown a lot of TG and SQ flights in the past. I've been upgraded on SQ for being *G and was told that was the reason for my upgrade. All my op-ups on TG were when crediting to TG, so I don't know how often they might upgrade other *G members, but my feeling is not so often, unless all their own TG Gold members have first been upgraded.

Personally, if I was choosing between ROP or SQ's FFP, and choosing between TG and SQ for flights, I'd choose ROP and TG.