First, in general, go for the full wizard. It's got pretty much the most support of any class, probably having nothing to do with the name of the company.
See, when I did that, I just focus fired the old DM a few times.
But to be fair, it was a Shadowrun game, and the old DM did play the mage, and, well, "geek the mage first."
If you're absolutely worried that he's going to fudge rolls so they always miss or always save, well, he *probably* won't do that, but you'll want to keep an eye out to see if they're missing each other or saving too often. If they are, and he isn't bitching about wasting perfectly good attack rolls ("Gah! Minion crit!" is a constant refrain from one DM), then you might want to have a talk.