I suppose you could always just compare prices...
...a few weeks back I had to go to TLS for a work thing there and back same day type of caper.
The choice (from LGW) convienently located about halway between Castle Rimmer and the Rimmer News offices is either BA or easy the schdules/frequency were very similar so how to choose? Easy, (no pun intended) go on the two airline's sites and compare prices - BA came out at £98 and easy £127...even before you add on the frills (which will doubtless progressively disappear but that's another story).
It's a no brainer. Seems to me the challenge the legacy (or network or whatever you want to call them) airlines have is perception - getting people to look at their prices in the first place (well that and massively reducing wastage but again another story yadda yadda).