I've forgotten some, as I have been on a lot of connecting flights with various different airlines, but these are the ones I can remember at the top of my head:
Scandinavian Airlines (SAS)
I've only had good experiences with SAS. Usually good standard and usually punctual.
Lufthansa
Only good things to say. Very professional, organized and punctual (and thus very stereotypically German).
Germanwings
Low-cost airline, but I had a good experience. Much better than a certain Irish low-cost airline.
British Airways
Flew with them back in the late '90s, but I only remember positive things about them. Though, the fact that it was my first time flying internationally probably made the experience even more special and exciting.
Air France
I don't remember specifics, but I feel like if I would have had a bad experience I would have remembered it, so it was probably a good flight.
Icelandair
I don't remember anything specific, but just like with Air France I feel like any bad experiences would have stood out in my memory so I'm pretty sure it was a good flight.
Norwegian
Good low-cost airline. There were no hidden fees or extra charges like that certain Irish low-cost airline. Got the job done in a timely fashion.
American Airlines
Everything felt quite subpar. Not terrible, but not necessarily great either. The plane was very dated. It was a fairly short flight though, so it was OK.
Delta Air Lines
Excellent, at least back in 2001 when I flew with them. The plane seemed very fancy, even in economy class. It was my first trans-Atlantic flight and it was the first time I was in one of those large planes with two aisles and three groups of seating in each row. I remember thinking that it was just like in the movies.
Midwest Airlines
Lots of seat and leg room, even in economy. Only had a positive experience with this one.
Trans World Airlines (TWA)
I honestly don't have any memory of what they were like. It was only a domestic flight within the US.
United Airlines
You've heard about people's terrible experiences with them, but I had a good experience on my trans-Atlantic flight. Maybe not the best I've ever flown with, but certainly not the worst.
Ryanair
Probably the worst airline I've ever flown with. Yes, they do offer (sometimes) insanely low prices on flights, but literally everything costs extra (even your luggage), so with all the added fees it's not that cheap in the end. Plus, they usually fly to airports in the middle of nowhere so you have to add the cost of traveling to the city you were meant to go to. Add the non-existent leg room to that and I'm not sure the supposed low cost is worth it in the end. I've lost count on how many times there have been issues of some kind or delays or other nuisances. They
used to be pretty good actually, but then they started cutting back on standard and upped the costs.