I've been doing some experimentation, and what I found the most fun was actually a 2x Lone Wolf run, with Fane as the main character, starting out as a traditional tank, but with summoning. Over time (without respeccing), I gradually turned him into more of a caster, as magic increases in strength later on (geo + fire is a very strong combo, especially for an undead).

His companion used a similar build, but with more of a wit/crit spell caster build (get the perk to allow for spell criticals), as one character with high wit is almost mandatory.