I would credit the AS flight to AS. There is an intra-Australia award chart on AS where a OW (on Qantas) is 12.5k in economy. I would work towards that award in the event you are planning any intra-Australia travel. You can also credit any DL or AA flights you take to AS (e.g., 2/3 of the US majors) and build your AS account to snag that intra-Australia

I would then keep your UR for eventual transfer for UA where saver Y is 80k/person roundtrip to/from Australia/New Zealand which is the best deal (and you can route via Asia in saver Y on *A partners if direct flight is unavailable).