Welcome to Flyer Talk
Adam Gawlowski 
Originally Posted by
MSPeconomist
The OP's decision isn't just between *A versus oneworld but also which specify airline to use as the primary program.
Going with *A but not UA has some advantages, including getting access to UA lounges for all *A flights, including UA domestic, at the *Gold level. Obvious disadvantages are no free Y+ and no free elite upgrades on UA (and probably extremely low priority for OPUPs on UA), no UA upgrade instruments, etc. if high enough elite status is obtained.
With non-US based FFPs there are generally less (or none) affiliated credit cards, less promotions, worse earn/burn rates. This is a generalisation not universal.
To the OP consider what you want from your airline (where do you fly, how often, what classes, etc.) and from your FFP (are status benefits important, award redemptions, upgrades, non-flying earning, etc.)?