codswallop-I'm not convinced. I have tried to play guitar with someone who could play recorder - yes they could but they weren't aware of the effect that air pressure could have on intonation-something of a learning curve. I have also played in a brass band-similar issue -you have to 'hear' the notes in relation to other players. This is what makes certain instruments difficult for learners. With regard to the 'best instrument' some instruments are 'in tune'with other instruments i.e. accordions, pianos, concertinas etc. This cuts down on the number of things a learner has to cope with.
As far as reading dots or playing by ear. I agree that both ways are the best route. I don't have too much trouble playing guitar by ear but concertina is a whole different ball game I wish it weren't tho it would make playing concertina a whole lot less frustrating.
chris