Check the fees. My wife had a 'managed' and 'unmanaged' 401k through Prudential and both of them were charging more than a percent.

Lookin' at a friend's Fidelity 401k right now (he doesn't understand this shit so he gave it to me to tell him what to do). They talked him into a T Rowe Price mutual fund that charges 1%.

One of the tricky things about funds is that yes - they tell you what's in there but not with a lot of specificity. "The S&P 500" - well, what does that mean? In a mutual fund, that means a synthetic blend of trades that model the S&P within whatever error bars they have buried underneath the fine print. With Vanguard it's probably very specific; right now, they're listing all their shit as of a week ago. With Fidelity? That's a quarterly prospectus. ETFs have, buried deep somewhere on the Internet, their daily .csv of holdings; I've found it for a couple of my etfs a couple times. Funds, managed or otherwise, will tell you that shit four times a year and in between, you really have no idea.