Cast the spells on Ozzie, Slash, and Flea. They're in both. Crono's Luminaire tears them apart. Serge's just... meh. His arrow is closer to Crono's Luminaire in terms of damage. And even with this, Serge is limited to one use of each of these spells in the battle while as Crono has multiple uses of his stuff. Crono can restore his magic easily. Serge, has to go to a lot more trouble to restore his elements.
But I agree with Delta Dragon, Serge COULD put up a grand fight. But overall... I still say Crono. Plus, even with magic out of the way. Look at Serge's range of sword techniques. Compare to Crono. Serge has about 8 different slashes. Crono has about 20. Top this off with Serge's average speed and Crono's "I'm Sonic the Hedgehog" fast speed.