I've noticed that Martins have a brighter sound, but then I've worked with Chris Amos who has a Martin so had plenty of time to listen to the difference. The rest of the time I am totally unable to distinguish one guitar from another, and often I don't really know a good player from a bad one.

I can tell the difference (by looking) between a Crane and a MacCann duet concertina, though, and I could probably identify several brands of melodeon just by listening :-)

I do agree that the quality of the playing is the important thing. Half the difference with instruments is what they feel like to the player. When Chris first got his Martin, his first comment to me was "it plays itself!". As a player that's often what you notice first, not necessarily the sound.

Anahata