I'm one of those that can ''read the dots if they already know the tune." Which is to say that the link between my ears and the keys is faster than the link between my eyes and the keys. That's a matter of practice--on the oboe, where I did a lot of sight-reading, those pathways are about equal. I play regularly in a gypsy swing group. I used to think improvisation was pretty much the same skill as playing by ear but it ain't necessarily so: as I often demonstrate, it is possible to shred on a solo only to fall flat on one's face when asked to play the tune.
When it comes to learning those tunes (the "head" in jazz parlance), I can and have gone either way--fakebook or ear.
Sometimes when I try to play by ear I blunder through it, playing ten times as many wrong notes as right. Other times I have what a friend called "copy fingers," able to mimic short phrases on the first try. I suspect the difference is preparation--warming up with scales to find the notes that will likely be employed--and really knowing the song--so that the blurs of notes in a fast reel can actually be hummed individually.
My current (overly-ambitious) project is to learn Swing Valse by Gus Viseur on CBA. This is a tune with many variations, and I've noticed myself struggling with the sheet music in places where it differs from the recording I know best. This may be a good tune to learn primarily by ear, with some aid from sheet music if I get stuck and maybe some of the embellishment improvised. Any tips?

Sometimes when I try to play by ear I blunder through it, playing ten times as many wrong notes as right. Other times I have what a friend called "copy fingers," able to mimic short phrases on the first try. I suspect the difference is preparation--warming up with scales to find the notes that will likely be employed--and really knowing the song--so that the blurs of notes in a fast reel can actually be hummed individually.
My current (overly-ambitious) project is to learn Swing Valse by Gus Viseur on CBA. This is a tune with many variations, and I've noticed myself struggling with the sheet music in places where it differs from the recording I know best. This may be a good tune to learn primarily by ear, with some aid from sheet music if I get stuck and maybe some of the embellishment improvised. Any tips?