Weboct 1, 2024 · the fidelity zero large cap index (fnilx) is one of the best index funds tracking the s&p 500. Fundresearch. fidelity. com next, we'll dive into the specifics of each fund. Webmay 31, 2024 · the table below introduces the best fidelity index funds with expense ratios no higher than 0. 20%.