From experience over the past 2-3 years, 60-90 sectors p.a., comments only on airlines where I've flown 5 sectors or more:
British Airways
Class: First, Business, Premium Economy & Economy
Ground Service: Efficient and usually pleasant - consistent
CC Service: Efficient and usually friendly, but the higher the premium, the better the service - consistent
Attitude: Generally professional
FF: Exec Club is a sales prevention process and the blue tier makes you feel like someone buying Tesco's stripy blue and red "value" brand
Other: Online check in is excellent
Verdict: I've flown with BA on only about 20 sectors in the past 2-3 years, as the Exec Club screws me
Lufthansa
Class: Business
Ground Service: Not always as good as it should be, e.g. Munich does not always support C class boarding easily
CC Service: Typically friendly and efficient
Attitude: Generally professional
FF: Stiff targets to gain entry
Other: Online seat selection is good
Verdict: Very good experience
Air France
Class: Tempo (Economy)
Ground Service: Highly variable, from very pleasant and chatty through to downright rude
CC Service: Usually efficient and friendly
Attitude: Gallic ( this has upsides and downsides)
FF: Part of Skyteam, which has an excellent FF scheme
Other:
Verdict: An acceptable experience
CSA Czech Airlines
Class: Travel (Economy) and Business
Ground Service: (CZ) Efficient and helpful, but often impersonal (UK) handled by an agent, but professional
CC Service: Generally as good as anyone
Attitude: Can be a little reserved, but this is in line with Czech culture and should not be misinterpreted as rudeness, rather it is polite and respectful behaviour
FF: A great scheme, silver tier after only 15 Skyteam sectors and Gold after 30. Regular upgrades to Business from Silver up.
Other: Nicely equipped and spacious lounge in Prague, twice daily service form my local airport to Prague
Verdict: My airline of choice, for Europe and USA, even if it means indirect flights
Alitalia
Class: Economy
Ground Service: Okay
CC Service: Okay, but not always on top of the job
Attitude: Pleasant
FF: Part of the Skyteam alliance, so good
Other:
Verdict: Very average, but by no means the worst
Ryanair
Class: ???
Ground Service: Efficient and fast
CC Service: Very friendly, not always very professional on the service side (although I don't question their safety proficiency)
Attitude: How many Stansted Express tickets would you like to buy?
FF: What's that?
Other:
Verdict: Does exactly what it says on the box, prices are consistently cheap, even at peak times and when booked only a week or two before
Easyjet
Class: ???
Ground Service: Typically long queues, but well managed and never a problem
CC Service: Quick, but friendly
Attitude: Please have the right money ready for the easyKiosk
FF: Don't be silly
Other:
Verdict: Can be surprisingly expensive, fullservice airlines often competitive