Upon further consideration, I recommend going all in "Mass Investors Growth Stk Fd-R4." It has a lower expense ratio than the S&P index fund, which is a good sign. That S&P fund has also matched or trailed Mass Investors Growth over pretty much all periods. If the S&P500 fund has a load you must pay then the choice is obvious: go all in the Mass Investors Growth fund, after first maxing out your IRA, HSA, and whatever other options you have with actual good funds. Side note, apparently Mass Investors Growth is one of the oldest funds in the country.