To my mind there is no question. If you are performing to an audience you should perform standing up,if possible. Unless of course you are a pianist or a harper ....

Performers who sit do not have the same impact on the audience as performers who stand, particularly if they sing.

Guitarists frequently feel that they cannot play to their best if they stand, but that obstacle can be overcome by practice. The list of virtuoso guitarists who are able to perform standing up is lengthy. Martin Simpson, Jack Williams and John James are just a few who spring to mind straight off.

Of course, OTOH, Leo Kottke, Doc Watson and Tony McManus are just a few who perform sitting down. Their performances are amazing, but IMHO would be better still if they were able to stand to play. Not that I expect Doc Watson to change at this stage of his career :-)

Those who limit their musical excursions to session playing, however, are probably better advised to sit while playing. Might seem a bit pretentious to stand up when it is your turn.

Murray