Depends very much on the equipment. There are items that grant the arcane acuity bonus (+1 to dc). One item works if you deal damage with fire spells, and I like to use that one for Wyll as warlock / either bard or sorcerer. You can stack this bonus very easily by upcasting scorching rays, getting a high dc quickly in battle. And since Wyll gets command from being a fiend warlock, he is effectively better at this than Shadowheart, unless you respec her to light cleric.
As a swords bard Wyll can also effectively use the other items, but I am a bit lazy and the
fire hat is easy to obtain.
