I'm planning a rtw and have already heard of the best lounges for each airline which is usually in their hub city/cities. For Qantas (SYD,MEL), Cathay Pacific (HKG), British Airways (LHR) and so on. I was wondering which lounges not operated by their own city people think are the best. For example, the terraces lounge (BA) in New York JFK seems to get good reviews. If people could comment on different OW lounges they've been to, it would be appreciated. Thanks.

The Terraces in JFK is about the 30th best Terraces in the world (out of the roughly 35 that exist), slightly better than SFO and much better than LAX (but the QF/AA lounge at LAX is considerably better than JFK, for example). BKK and SIN have good lounges (both CX and QF/BA). NRT has a surprisingly poor lounge, but TPE has a great CX lounge (mini-wing). But lounges change all the time (the new CX lounge at YVR is very nice, moving YVR from poor to above average -- but that lounge isn't available when flying BA or AA, only CX). However few lounges are good enough to be worth a special visit, this isn't really a meaningful fringe benefit of OWE travel.

I like the AA lounge in SCL the best, probably followed by the BA lounge in SIN and then the CX lounge in TPE.

I like the BA lounge in JNB also although I know that others don't.

I LOVE the First Class lounges in HKG (EXP's have access to FC). They have a buffet meal dining room with nice cooked meals, sandwiches, salads. Beautiful showers. Attentive staff (they walk around with a tray and take and fetch your drink order).

And actually, the LAX AA Flagship lounge is nice. And BA Concorde lounge in Heathrow is ok.

BA FIRST CLASS lounge LHR... Staff very attentive, Flat Screen TV, Very good selection of magazines and food very very good. Also the best place to see a star... I have run into J.LO, Madonna, Jerry Hall, Elton John, Donatella Versace over the last 3 years...

If in T4 then I suspect you mean the Concorde Room, which is the real First lounge. The one that is called the First Class lounge is nothing of the sort - it is for BA Gold and OneWorld Emeralds travelling in economy or business. I suspect the people you mentioned travel paid First.

Of course the term "foreign" is all relative to one's nationality, but I'll assume you mean non-U.S..

I think the all the usual suspects for great OW lounges have been covered. I agree with the positive treatment of the SCL AA Admirals Club. Much nicer than the LAN lounge, which is surprisingly dissappointing for such a world class carrier. I've also not been overly impressed with the QF F Lounge in SYD.

Although technically not a OW Lounge, the lounge that CX uses at DPS is fantastic. IMO right up there with the Wing and Pier. It has a full buffet, comfortable seats and an outdoor terrace overlooking the ocean and the runway.

I read the OP as assuming that unless otherwise specified, the best OW lounges in SYD would be QF's, the best at LHR would be BA's, and so on - and then asking where were the best lounges outside the home country of the carrier involved (eg his example of BA's lounge at JFK). So CX's lounges at HKG and BA's LHR lounges don't count, while CX at DPS, AA at SCL and BA at JNB (as mentioned above) do.

Yes... The Concorde room to the right past front desk.

Not sure if I agree about the CX lounge in SIN. I realise it was about to be renovated so I am probably a few months out of date here, but last time I went there, found it a broom closet so quickly sought refuge from the QF/BA lounge which whilst huge is fantastic (particularly the showers). When I last was in the CX lounge, found it dark, small (although that can be a good thing) and the food etc pretty dismal - Quite in contrast to normal CX offerings!

CX has an excellent F lounge at BKK but not at SIN, while QF/BA have a good joint lounge at BKK in the old airport (presumably better in the new airport when it finally opens) and an even better one at SIN. My wording was sloppy, QF/BA at SIN is worth seeking out, CX is not (though still better than the NRT lounges for any airline, including JAL, to put it into perspective). Most of the time I've been using the SQ lounge when in SIN, otherwise I route via HKG.
Most lounges are dismal. As a group only the BA Terraces are noteworthy with some attempt at a consistent standard but even they tail off quickly and there are less than a dozen good ones (out of the 30+ Terraces). For F lounges none of the publicly available ones are really noteworthy, they are mostly what the J lounges should be but are not. LH with their new F facility at FRA has really raised the bar but it doesn't look like Oneworld feels compelled to respond yet. I've started using LH trans-Atlantic and they've been significantly better than BA.