Which OW airline's FFP is it easiest to reach the Gold Status?

Which Gold do you mean? "Gold" is the lowest status on AA (OW Ruby) and the highest status on BA (OW Emerald) and the middle status on QF (OW Saphire). So it is easiest on AA particularly as AA has the Gold challenge (search on that for details). However AA Gold has negligible benefits, why would you want to reach that? Presuming you mean BA Gold, the answer varies with your fare basis. If flying paid J and F fares it is very easy on QF (you can do it with 2 round trips but lots of dollars) while on AA it takes 100K miles (66K if flying entirely in F -- still more miles than QF requires though QF is not miles based).

I'm going to assume he means something equivelant to Star Gold, that is, oneWorld Sapphire.

The clear answer is AA, via the Plat. (OW Sapphire) Challenge...

Not so clear, depends on metrics and what you are trying to minimize. In miles AA normally costs 50,000 miles flown, in the challenge that drops to 20,000 miles or 10,000 qpoints. But on QF it is possible to earn QF Gold (OW Sapphire = AA Plat) by flying as little as 3000 miles (without a challenge). QF status is not based on miles, but on "status credits" (these very loosely equate to revenue for QF). And the non-AA Sapphires are worth more than AA Plat (at least for those who travel a lot on AA) as they provide free AC access while Platinum does not.

I'd love to hear how you did that 3000 miles= Sapphire. Lots of LAX-SNA type segments, perhaps?

But, remember QF does not give status without four QF segs. Could be quite hard if not in Australia. Normally AA caries this restriction, although it does not apply to a challenge...

We've agreed this restricution is never enforced:

http://www.flyertalk.com/forum/Forum39/HTML/000861.html

I earned my QF Gold=Sapphire the old fashioned way (international F). It took 10 days (and less than a month to reach Emerald). But as an academic exercise, someone in Australia commuting SYD-MEL on J fares would earn Emerald after 12 round trips (routing SYD-CBR-MEL) and can renew after 10 round trips in subsequent years. SYD-CBR-MEL is 438 miles, so this is 5000 miles. SYD-MEL is the most heavily traveled route in the world (more passengers than LGA-DCA or SFO-LAX!) so this is a realistic scenario. QF has other (shorter) routes, such as SYD-NTL (103 miles) so it is possible to do NTL-SYD-CBR-MEL which would make Sapphire at 3600 miles and Emerald at under 8000 miles. I'm sure it could be done for less. While on AA it is a minimum of 66,666 miles (flying excusively F fares) or more commonly 100K miles. But much more fun to fly JFK-SYD-HKG-LHR-SFO-BOS-JFK which would also earn Sapphire provided it is flown in F.