Hello. There's obviously loads of theads on this debate, but can't find much on the pro's and con's on each from a pov of a UK resident.

I'm currently platinum on AA and fly to US 3/4/5 times per year from LHR. Are there any reasons why I should consider a switch to United, especially maybe with the UA/CO merger happening soon? Are there any mileage accrual percentage tables for mileage plus when travelling on star alliance carriers?