Who knows what will change the most. But Easyjet will definitely change. McCall is being very clear and open about that already, whereas the BA management are keen to keep things largely as they are (http://www.telegraph.co.uk/finance/newsbysector/transport/8785035/Keith-Williams-has-steered-British-Airways-through-some-tough-turbulence.html)
What's more, McCall is actively trying to position Easyjet somewhere in the middle between low cost carriers and national carriers. Something not really achieved by anyone to date. If successful it will no doubt be very successful, but untried water in this industry is always risky. If it doesn't work then what......? Of course BA may change too, but of the two airlines Easyjet shows the most sign of changing at the moment for sure.
Also, BA has a strong union backed rostering policy that will take some fighting. That will undoubtedly slow down any change, even if it doesn't resist it.