One thing I would be on the lookout for in an audition is what amplifiers are being used with the particular speakers. Unsound is absolutely correct that you get the speaker that sounds best to you, but if you have a low-powered tube amplifier and the speaker you're listening to requires a powerful solid state amp to sound its best, you'll need to factor the possibility that you might have to buy a new amp into your buying decision. Perhaps the dealer giving the audition has a number of amps that you could listen to with the speakers in question. In addition, if you have space or placement constraints in your listening environment, you might take note of where the dealer has the speakers placed in the room, how far from the walls they might need to be, how big a room is used, etc.
Otherwise, I would bring my favorite discs/records with me to the audition, not necessarily the best sounding but the ones I love to listen to, and see how they sound on the speakers. Each of these speakers is an excellent one, and each will have its strengths and weaknesses and its own particular sound. Rather than trying to analyze different aspects of the presentation from the speakers, I'd suggest that you just try to listen for the one you feel sounds right to you, that connects you best to the music. That's really what you want, when you come down to it.
Otherwise, I would bring my favorite discs/records with me to the audition, not necessarily the best sounding but the ones I love to listen to, and see how they sound on the speakers. Each of these speakers is an excellent one, and each will have its strengths and weaknesses and its own particular sound. Rather than trying to analyze different aspects of the presentation from the speakers, I'd suggest that you just try to listen for the one you feel sounds right to you, that connects you best to the music. That's really what you want, when you come down to it.