Different Airlines

You will find that most people will have had positive experiences with those airlines and then a few have not. Irregular operations can happen with any airline, but most do a good job.

To where in Germany do you plan to fly? Airfares vary not just based on the airline but also when one has bought the tickets.

I fly Delta nonstop between JFK & Frankfurt. Now that Delta has started nonstop service between JFK & Berlin, I will take that either next year or in 2025.

I only fly nonstops.

We flew IcelandAir to Frankfurt in May after British Airways cancelled our flight a few hours before take off. It was fine. It is more of a no frills carrier than it used to be so you pay for those airline meals if you want to eat.

I fly only to FRA from SFO when I decide to fly to Germany. It has been several years since I flew Lufthansa. For better or worse from SFO to FRA, I have been flying United in Basic Economy, the overnight flight, the non-stop eleven hour flight, arriving slightly before 10 AM.

Next summer's trip I've not decided yet, either to FRA or Paris CDG.

There are a couple of rating organizations online if you want to get a broader impression

https://www.airlineratings.com/passenger-reviews/turkish-airlines/

https://skytraxratings.com/airlines/turkish-airlines-rating

https://www.forbes.com/sites/alexledsom/2023/06/05/airline-ratings-worlds-best-airline-2023-awards-air-new-zealand-wins/?sh=5a4751b73fdd

I have flown all on your list except Iceland Air, and Turkish Air is my second favorite airline. My favorite airline is which ever is the cheapest, cause they will all get you there. But if you want a little nicer experience, Turkish Air has always done that for me. Among my least favorite is Lufthansa, but they are cheapest sometimes so I fly them fairly often.

I will take almost any European airline over most US airlines, but to be honest I don't look that closely if it's one of the major carriers. You will have good and bad experiences on virtually any airline.

I have flown many of the major carriers to northern Europe--Lufthansa, Air France, KLM, Delta, SAS, Condor, United, IcelandAir, British Airways, Finnair, American, Aer Lingus, Turkish, and ones that no longer exist. Maybe more, and definitely more within Europe (RyanAir, etc.) I can't say that I can pinpoint any that were stand-out good or bad.

Fare classes vary dramatically, so prices are a matter of when, through whom, and which fare class you book.

It has been many years since I have flown Lufthansa, but it was a good airline 40 years ago.

We live in South Georgia and mostly fly on Delta/KLM/Air France. Delta in my opinion is the best US airline. United is second and American third.

Air France is fantastic and prefer it when connecting in Europe.

TAP was nothing to brag about, and Iberia was one to avoid.
I hear from friends to avoid Air Italia.

I have heard positive things about Turkish Airlines.

We did a Safari last year in Kenya and Tanzania and flew to Amsterdam on Delta, then used Qatar Airways to and from East Africa. We had one long layover in Doha, which involved getting a hotel for several hours. The flights were generally OK, the food was actually pretty good. However, on two of our four flights either mine or my wife's screen to watch movies didn't work and nothing was done to fix it. I think they just didn't function. Also, on our last flight, I was moved from my aisle seat (already had the boarding pass for it) when I checked in (with no explanation). I politely asked why I was moved to a middle seat and the attendants were very rude, saying you don't own the seat, we have the right to move you. We will never fly again on Qatar, despite their low rates.

Egypt Air, we took because it was included on a tour of Egypt. We flew from JFK to Cairo. It is the only airline that flies directly from the USA to Cairo. The flight to Cairo was 17 hours late leaving and we were told by someone in the know that Egypt Air does this every six months or so when their airplanes need servicing in NYC. Because of that we had to stay a night in NYC and the reimbursement for the cost was not enough. Also, while on the flights many times getting an attendant was very slow or impossible.
Don't fly Egypt Air.

We have flow on Korean Air Lines and it was great. The food, service and comfort was super.

I always use Kayak.com to check for flights and then book directly with the airline. Usually Delta is our pick, unless we can save. Usually Delta, United and American are about the same.

Also, I have heard positive things about Icelandiair.

I wouldn’t take the fact that your German cousin’s fare was cheaper than yours as a negative thing. We’ve found over the years of exchange homes with families in some European countries, they often pay much less than we pay for the same tickets in reverse.