Thats a tough question, each one of the often mentioned airlines compete fiercely for the top slot but being a frequent flyer for 30 years I have found inconsistency amongst the top airlines their biggest enemy. BA
have more all around achievements, but they too are victims of their own success due to their size (..often, their left hand does not know what thier right hand is doing.) The smaller airlines like SAS are also noteworthy.
The US airlines simply do not make it, very erratic and flight crew are like school teachers, constantly telling you what to do or not do and indifferent ground staff, flying within the US is like being on a greyhound bus with wings.
In my (humble) opinion, the best airline would have the following traits;
Efficiency like Lufthansa
Comfortable seating like British Airways
In-flight meals like Swissair
In-flight drinks like Air France
Friendly flight crew from Singapore Airlines
On-time performance like JAL
Competent ground crew like SAS
Frequent Flyer program like American Airlines
Clean aircraft like Emirates
Baggage handling like Lufthansa
Safety like Qantas
....and fares like Iran-Air.