Another welcome here to Flyertalk !!
My suggestion is United and the Star Alliance.
While there is indeed risk here lets look at the bright side of things.
A world class program United offers you many unconditional earning opportunities with a wide variety of opportunity when compared to other programs. Only One World is in the same league IMO.
Better cabin seating in many situations and more professional flight crews.
Though in this industry it certainly can vary on a given day.
Lots of labor unrest at many carriers these days.
Though I find United frontlines to be and remain professional and private as of late regarding all the recent concerns.

I believe or expect that US Air will be the first among the current carriers to be among the missing over the next year or months unless a miracle happens.I stand to lose 80k with them.
My suggestion is to have an exit strategy push come to shove should you need to exercise it. Perhaps a way out through Diners Club or a ticket booked once you reach the required redemption amount.
The Inside Flyer Team will hopefully keep us posted on any red flag emergency warnings or bulletins regarding the fate of any carrier that may perish.
But for today you will really appreciate the Star Alliance lounges as a greater & perhaps better alternative to One World.
Not to mention much more comfort and your travel sanity flying with Star Alliance a well managed Alliance.
Milegae Plus customer service is outstanding and always answers the phone and is toll free.I won't get into beating up the others out there.
But you would be surprised at the lack of concern for their customers and frequent flyers. I find many of their rules and penalties to be unacceptable in and out of the program and as a result they lose the lions share of my business every year. The majority of folks I find happy in those programs either have no choice in their choice of travel or haven't flown significantly on Star Alliance or One World to see all the exceptional aspects and benefits that exist. Including supperior reward availabilty(See recent IF study)
Good luck in you decision process.Happy Safe Travels