My nehew called me after taking a new job requiring him to be on the road internationally 1 week a month. To him, FF programs are 'so confusing'.
So he asked me to help him pick a primary airline to credit 'miles' to.

He will be travelling to SIN, PEK, SHA - EZE, RIO,SCL - IST, FCO, VCE. So these look to me to point to OW. (He is concerened about UA going to a revenue basis, but I suspect AA will get there in a year or 2 also).

Now the details:
His company buys him 'cheap, bulk, coach tickets'. They use CX a lot because they "give his company very good deals". AS is important to him as he and his gf have relatives in Alaska.

So, to me AA or CX would be a good fit. He is far from a veteran traveller and I perceive that a major goal should be to get to Saphire status as quickly as possible for lounge access. Of course collecting miles for him and his gf to travel is very important.
Any suggestions, along with the reasoning behind them would be appreciated. I know a lot about Star Alliance and Sky Team, but zero about OW.
Edited to add: Home airport is LAX