With an IRA, you lose the financial advantage of group buying power, says Bogosian.
Many funds come in two flavors: institutional and retail. Most individuals don't have the required minimums to get in the former, so they must buy retail funds.
"Most 401(k), 403(b) and 457 plans have significant buying power -- much more than the individual," Bogosian says. His advice: "Look before you leap. You could be paying more for exactly the same thing."
But be careful that you're comparing apples to apples, says Slott. It's often difficult to determine the fees charged by 401(k) plans.