Anything colourful or different works the best for me, especially if one airline has multiple colour schemes. I love anything that has as little white as you can possibly see on an airplane, white is just so boring. I would love to have photographed all the BA Utopia tails but alas, a very boring old lady with too much to say helped kill those. Come on people, live a little and add a little colour to your life and that is coming from an old guy getting set to retire soon!
I also sorely miss the cheatline. If an airline insists on dulling up an airplane with white, at least break it up a little with a cheatline or even better, two or three of different colours. I admire any airline that introduces special colour schemes and one offs, gives a photographer like me something to live for and chase after and even for the scribblers, individual schemes have gotta make your life easier as well.
I guess by airline, my two favourites from the past were Western Pacific and Braniff, especially since the latter flew the greatest airplane of all time as well. I am so glad that for the most part my all-time favourite airplane saw it's best days back before boring became so common in airline liveries, long live the 727 and lotsa colour in you livery! Of today's airlines, NOK Air looks promising so maybe have to see what I can do about heading to somewhere I might see some fo their colourful airplanes.
Anyway, that is enough of a rant for now, have to get off the sopabox and see if I can capture one of my current favourites, the one daily Frontier here in Vancouver.
Cheers Steve