I know I've read the answer to my questions over the past 6 months, but I can't seem to phrase the right search to find it.

On Thursday morning I have about four hours between arriving in LHR on AA (cheap ticket, upgraded to business with eVIP) and leaving for Hong Kong on CX at 12:45 PM (a DONE4).

As an AA EXP I believe I can use any of the OW lounges - where should I head? The obvious answer would seem CX's - but the obvious answer is sometimes not the best answer.

And more generally, since I hold a Qantas Club card, are there times when I will do better showing that rather than my EXP card? Right now I only ever break out the Qantas Club card in the US on domestic trips.

Thanks in advance for any insight.

CX only recently opened their lounges at LHR and they are modelled (so I read on their website) on the HKG lounges which are superb.
The AA Biz Lounge at LHR is getting very "tired" these days.

I don't think it would matter which card you flashed as long as you are EXP you would get into either. The US seems to be the only place where getting into clubs is a problem (for non-international travel).

I am looking forward to checking out the CX lounge at LHR next week!

You arrive in T3 and leave from T3. The CX lounge happens to have very nice showers -- better than the AA Arrivals lounge -- but might not be open when your AA flight arrives (they do open about 4 hours prior to the CX flight departure times, so it would be close). Getting to the AA Arrivals lounge involves going landside through customs and is probably not worth doing. Going to another terminal to use a lounge is technically not allowed (sometimes it works but usually does not). In your circumstance it really isn't worth the hassle, use the CX lounge. It has slightly better food/drink than the Terraces or the FL and much faster internet terminals (also more internet terminals than all the AA and BA lounges put together; not quite true, but close). The CX lounge is by gate 1 in T3 (a bit out of the way).

Thanks Number_6. CX it is. The directions are helpful. In IST I walked about one mile it seemed looking for the BA Lounge, which turned out was back near immigration wher I had started!