The main thing about these two mutual funds is price and performance. These are no load passively managed index funds held by Vanguard (VTSAX) and Fidelity (FZROX).
VTSAX is an index fund that tracks the total stock market. It holds around 4000 different companies. It is very tax efficient, and it is the best of the best at Vanguard.
FZROX is a newer fund created by Fidelity. It has a $0 minimum and 0% expense ratio. In the fee wars, the companies have made another type of fund with zero expense ratios and, therefore, zero fees