Jet2
In respect of the potential Jet2 v Ryainair battle, then the winner would be the one who can offer a fare on the first screen of the booking engine that is the price you pay. For example, Leeds - Malaga, £75 including check in, payment fee, suitcases etc. How easy would that be? I have also in the past found fares with BA ex Manchester or Birmingham to be cheaper than any of the low cost carriers and a straight forward fare displayed.
It is increasingly difficult for us to compare fares on a true like for like bases.
I have experience of both airlines and must say that I have never been more than a few minutes late with Jet2, with Ryanair being equally punctual. I have had trouble at EMA though when checking in with a bag that was ever so slightly overweight. I know rules are rules though.
If a battle does ensue at Leeds, then I see the larger operator being the winner. Look at similar cases in the past, with airlines, bus operators, ferry operators and so on.