As a BA FO, I think there is really only one huge advantage to BA (apart possibly from job security). It is choice you decide your roster, what fleet you fly, even which seat you occupy. BA cannot (if you stay within the rules) assign you anything its entirely up to you and your seniority.
There are other more minor advantages. such as the money eventually been quite good, and you are generally very well looked after. Anyone who has worked for another airline knows that.
Obviously the pension has gone these days, although the new one is ok when compared to other defined contribution schemes.