What airlines have you used and or seen?
I have used Southwest, American airlines Eva air, delta. I have seen All Nippon, jal, United, air India, American airlines, Cathay dragon, Cathay Pacific, Delta British airways, Spirit airlines, KLM air Canada, Envoy air, air France, Thai, JTA.
I have used Swiss, Iberia and Edelweiss.
I have seen …many many many airlines… countless 
I’ve seen countless airlines, and wouldn’t even know where to begin listing them all! 
But I have been on:
British Midland (latterly BMI) (defunct)
BMI Regional (it was a separate airline)
BMI Baby (defunct)
FlyBe (including a trip back in the day when they were called Jersey European)
MyTravel Airways (defunct)
Aer Lingus Regional
Aer Lingus
Jet2
Brussels Airlines
Virgin Atlantic
KLM Royal Dutch Airlines
easyJet
British Airways
Vueling
I’ve got plans to fly with Loganair and Eurowings in the near future.
I have used Croatia Airlines, Austrian Airlines, Travel Service, Smartlynx, Air Slovakia, SkyEurope and Danubewings. I dont even know how much I have seen.
I have been on :
Iberia
British Airways
Swiss International Airlines
Air Europa
Monarch
EasyJet
Tarom
Lufthansa
Let me see…
Been on British airways
Lufthansa
Air France
Delta
JetBlue
Alitalia (worst one, sorry Italians 
)
Bulgaria air
Iberia
… can’t think of any more…
Been on:
US Airways
US Airways Express
Piedmont Airlines
PSA Airlines
American Airlines
American Eagle
Republic Air
JetBlue
Icelandair
United Airlines
Seen:
Southwest
Finnair
Emirates
Etihad
Air France
British Airways
Virgin Atlantic
Virgin America
Alaska Airlines
Delta
Delta Connection
Iberia
Aer Lingus
Ryanair
Easyjet
Air Canada
Aurigny
Flybe
BMI
Thomson
Thomas Cook
Condor
Hmm…
Been on:
British Airways (4 737-400, 2 A320)
easyJet (4 A319, 4 A320)
Thomson (now TUI air Britain) (2 737-800)
Will fly Jet2 next spring (737-300).
Seen too many to list!
I had only seen Wizzair IRL.
Bine ati venit in Romania 
Now…if I had to say what airlines I had seen in general over media and photos…there would be a lot more.
Been On:
Thomas Cook
Thomson
Jet2
British Airways
South African Airways
SA Express
Airlink
Virgin Atlantic
I have been on:
Transavia (Boeing 737-800)
Arkefly / Arke / TUI fly (Boeing 767-300, Boeing 767-300ER, Boeing 787-8)
I want to fly with:
KLM Royal Dutch Airlines
I have seen:
Transavia
Arkefly / Arke / TUI fly
KLM Royal Dutch Airlines
Air France
British Airways
Iberia
Easyjet
Flybe
Delta
Emirates
China Southern
Turkish Airlines
… And many more…
Flown with:
Delta
Northwest
United
US Airways
KLM Royal Dutch Airlines
KLM Cityhopper
Martinair
Lufthansa
LTU
Air Berlin
Germanwings
Wizzair
Brussels Airlines
British Airways
Condor
That’s it and I have obviously seen a whole lot of other airlines as well 
SAS
Iberia,
Ryanair only once never going back
Easyjet
Maersk Air
Thomas Cook Northern Airways
Premiair
Air France
British Airways
Onur Air
Swiss Air
hmm thats about it not so much flying out of cph hehe
Been on:
KLM
Transavia
Ryanair
North-West (merged with Delta)
Delta
Air Canada
US Airways
Finnair
SAS
And I’ve seen way to many to make a list lol
Oh, that list is yet quite small for me ! 
German airlines:
Aero Lloyd (A320, A321) - defunct
airberlin (A319, A320, 737-700)
Condor (A320, 757-300)
Germanwings (A319)
LTU (A330-300, A320) - defunct
Lufthansa (737-300)
Foreign airlines:
American Airlines (757-200, 777-200ER)
Emirates (A380, 777-300ER)
Qatar Airways (A320, A321, A330-200, 787-8)
To be added:
Air Algerié
Air Seychelles
and many more 
I’ve flown American, British Airways, JetBlue, Delta, United, Southwest, Air Canada, Aer Lingus, Alaska Airlines, Hawaiian Airlines. Not many but I’ve flown plenty of aircraft!
Probably seen too many to list, but as to airlines I’ve flown, I thought I could add a more Australian flavour 
Air Canada
Air New Zealand
Delta
Jetstar
Malaysian Airlines
Qantas
Singapore Airlines
United
Virgin Australia
Of these, I probably fly Virgin Australia and Air New Zealand most frequently 
Many aircraft types and routes. Yet to log an A350 though!!
Flown with:
Alitalia
Meridiana
Eurofly (merged with Meridiana)
Air Dolomiti
Iberia
Air Europa
Easyjet
Ryanair
Lufthansa
Emirates
Delta
Klm
Sas
Finnair
Ana
And seen more
Been on:
Thomas Cook
Thomson
First Choice
FlyBe
Jet2
Privilege Style (on behalf of Jet2)
Air France (operated by British European)
Swiss
Air2000
British Airways
I have Used:
Qantas, JetStar, Tiger Air Australia, Air New Zealand, American Airlines, British Airways, Virgin Australia, Emirates, Qatar Airways, Singapore Airlines. I most frequently use the Australian Domestic ones like JetStar and Qantas, but I use Tiger Air for Cheap (Very Cheap ) and when I travel overseas my family and I try to catch a different airline every time, so that we get a different stop-off city (Singapore, Dubai, Doha).
I have Seen:
All of those^^^, too many to count (I always look for new ones when I travel ), and I check stuff online as well.