Les Paul, straight in, at the very least. I say this because it'll likely please most demographics, though I would like to hear some single coil guitars too.
EQ them to sound the same. Then EQ them each to show strengths and especially differences. The way these amps ate marketed, it does make it look like the only difference is the full EQ vs shape control.
as soon as i typed that, i left for school and i thought about that too. yeah, honestly i'd like to see something like Ade's old demos (but with a Les Paul, Tele, Strat, maybe one other guitar). honestly those videos is what sold me on both of my amps.