Depending on who weilds them it could be either. I'll give the Excalibur to FF1 Knight and the Ultima weapon to Cloud and its obvious. Now for fun, give Vivi Ultima weapon and Rosa Excalibur and theres a duel!

Since you can't pit weapons against eachother without specifying users thats really not a valid battle. The 2 swords would just lay there, thus draw.

Sephiroth and Cloud vs. Cecil, Freya, Yuna (FFX-2) and Guy