Gia, it doesn't really matter. An index fund is designed to perform exactly as a particular index. You may want to invest in certain sector index funds, but that kind of defeats the purpose of index investing. Your best course is to invest in a broad index fund like the S&P 500. An index fund's performance will essentially duplicate the performance of the index itself, so it doesn't really matter if you go with Fidelity, Putnam, etc.