In Europe, I have flown with:
EasyJet
Air France
Lufthansa
KLM
EasyJet - Outbound from base on the first flight, fine. On time, clean aircraft etc. Inbound on later flights in the day, awful. Delays, aircraft untidy and rather dirty, with stuff on the floor and rubbish in seat pockets etc. Not overly impressed with them, all be it the leg room was passable and crew were pleasant.
Air France - Out of 4 flights, 2 resulted in broken bags, 1, bag went missing for 4 days and the 4th I missed my connection because the flight was a Hop! regional flight and it took ages to get through connections, even with a healthy 2 hour connection at booking.
Lufthansa - Fine. No issues, on time, planes immaculate, crew ok, dislike FRA with a passion though. Novel to fly the CRJ for the first time though... Cosy!
KLM - Baggage delayed on 3 out of 7 flights, which is why I really dislike itineraries with a connection as it just adds to the possibility. Their E190 fleet is very spacious and comfortable and had pleasant experiences onboard. Not a fan of AMS and the bussing operation for the CityHopper flights which sometimes I end up on. One big bonus was that I got an upgrade to Business for €260 from AMS to ACC which was a bargain.
I think they all have their issues, and if I had the choice of a direct from the UK with BA, or a connection with another, or with Easy, I would stick with BA possibly part due to familiarity, but also cuts out connections, the time they add and the possibilities of lost luggage etc.
Just my thoughts and experiences.