I know CC that have transitioned from easyJet to BA and viceversa.

The main reason to switch to BA is the opportunity to travel around the world.

The couple I know that were at BA (after working a couple of years) and moved to easyJet were for schedule and stability reasons. Both worked at BA, but management refused to "marry" their schedule (so both barely saw each other). With easyJet, they are based at Luton and they know that pretty much every-night they will sleep at home, whether they had duty or not.