I agree, Market Force, for a NEW IC. Market Force would not be my recommendation for an experienced shopper, but I think they're ideal for a newbie.
I'm not a fan of Performalogics.
silverchic, I do not do the audits for MF. Although they all seem to get scheduled pretty quick every month, and I hear from other shoppers that they like them, I do not think they are worthwhile. I prefer their regular mystery shops, and I pick and choose to get the ones that are worth it to me.