I was EXP for many years and for a time with BA Gold alongside it but I largely dumped AAdvantage after the programme was butchered 2 or 3 years ago. As I've now pretty much exhausted all my many AA miles I will miss the very low fees on redemptions against what BA want to charge for the same trips but probably very little else.

As always with these things, there is no one-size-fits-all answer to this question though.