The Airlines will be consolidating this year so I feel you will be better off staying with United's mileage plan. This will be another year of consolidation and unfortunately it will mean higher prices for us and less benefits in the airline industry. As a note of financial situations the airlines seem to blame everyone but themselves of this problem but if they would find decent things to charge for like Wifi, high speed internet, or things business people need then we might see an airline start to profit some.
I would just stick with the program you have now because its very rare that an airline loose its frequent flyer mile programs in any bankruptcy unless its some smaller airline.