While the choice of Arts has some strategic interest, it's over before the battle even begins, and then it's just a series of dice rolls with, at most, a choice of whether and how much raw vis to expand.
The best rules I'm familiar with are letting the phantasms allow you to shift the Arts of the cartamen, so that the image is important. For example, a Rego Ignem certamen might start with Flamis of Fleambeau's phantasm being a ball of fire, which sends tendrils trying to burn more stuff, while Cjorn of Bjornaer chooses a fire seprent that tries to coil around the ball and squeeze it. On the first round, each player has to choose how much of his power he is going to spend on Attack, Defense, and Shift. The guy who wins the shift can shift one Art to an appropriate direction, as indicated by the warring phantasms. The Flambeau mage can attempt to shift to Creo Ignem, as his ball attempts to expand and enflame the serpent; the Bjornaer can attempt to shift to Rego Animal, as his shape is that of a serpent. There is a tactical choice in how much to expand on each of the three aspects (Attack, Defense, and Shift), and some measure of storytelling and stuff happening in the game-world by embroiling the story of the battle in the mechanics.
Unless someone comes up with a better idea, I'm going with that - but the problem with it is that it neuters the benefit of having two or four high Arts, and that the mechanics are completely untested and very possibly unbalanced.
