If you believe markets are generally efficient and prefer to invest in an index mutual fund to achieve an index-like return, shopping for the best index mutual fund based on low fees and a low expense ratio makes good sense. The portfolio manager of an index mutual fund endeavors to invest the fund's assets to track the index as closely and cost-effectively as possible. Larger index funds have an advantage in that they can spread their operating costs over a larger asset base.
If you somehow missed the best 30 months, your $10 would only be $154. However, if you managed to miss the 30 worst months, your $10 would be $1,317,803! Thus, my point: Missing the worst periods has profound impact on long-run compounding. There are times when you end up better off by being out of the market.
Interestingly enough, if you missed the 30 best months and the 30 worst months, your $10 would still be worth $18,558, which is 80% higher than the buy-and-hold strategy. This all comes about because stock prices generally go down faster than they go up.
This type of IRA allows you the most flexibility. You may roll the proceeds back into a 401k plan if you want to utilize a loan provision. However, for tax reasons you should not make annual contributions to this IRA. If making annual contributions becomes important to you, simply open another contributory IRA.