Well No. 1 for me is EasyJet
Had dozens of flights on dozens of routes with them and rarely am i disappointed.
Monarch i use twice a year and I like their service but just cant get a 'cheap/low cost' flight no matter how hard i try.
As it happens i take my first flight on BMi Baby this month from EMA
I am looking forward to it even though they use ageing 733's.
Ryanair ive used lots too and pretty much a different argument here, the service has always seemed below usual standards, overall the flights i get on the website are not necessarily expensive but always far dearer than the price that is shown first when they've stuck their add-ons to the bill. I,m expecting before long that they will want to charge you for each breath you take. Therefore they will not get a rating from me.