The light saber would sadly win because it is like a laser and it would chop Excalibur in half, easily. So this isn't a fair fight... If the light saber was plastic, then, Excalibur would win
I would not be so quick on that statement. According to legend Excalibur is invincible. A lightsaber can not cut through something invincible. Though I would still prefer the lightsaber, you can turn it off and it is lighter than a sword (thus it is quicker and more of a surprise in a fight).