Agree with British Eagle. One from the obscure past : Treffield International. I also used to like the older Ethiopian scheme. BOAC as well.
In fact, I think almost any airline from the 1960s and 1970s looks good. But then maybe I am just showing my age. Today I think there's just too much white, too much junk in the form of dot.com titles, picture decals, lower case names and too many wavy lines. Some aircraft today look like fruit salad.
I also think it can depend on the aircraft type. Almost any airline colours on a Constellation looks terrific, especially TWA. Any DC-4 or DC-6 from the 1950s the same. Today ? To be honest, I find it hard to fault the current British Airways scheme, but that sounds a bit boring !