TSLA
also "best" is an ambiguous, meaningless phrase in investing. you need to decide what your goals are and what level of risk you're comfortable undertaking. there are no universal answers here beyond "low cost broad-market index funds are a good thing", of which fidelity provides plenty.
I go with CISIX. It’s similar to the SP500 but not the exact same. Target funds would be the obvious go-to choice, but bonds have not behaved properly during the pandemic, so I kinda lost trust on them. I’ll probably switch to target funds later on though, if they start to behave. In all cases, see what is actually available in your 401k plan. It doesn’t have all the funds and it may depend on your employer’s deal with Fidelity.
FXAIX. if you are young, do some large cap growth funds as well.
I do the same on my brokerage account and HSA. It’s not available in my 401k and CISIX is the closest. How do you choose between holding FXAIX and buying the SPY ETF?
Expense ratio (0.02% vs 0.09%, i.e. ETF is 4.5x as expensive), but ETF can be traded whenever, while mutual fund often has penalty if you held shorter than X days. So, if you have/want long term investments (at least a couple years), mutual funds
Target date index funds. Until your assets are above $500k, keep it simple.
Assets above $500k here. What to recommend?
Target funds are conservative and very expensive. Try their 0 expense funds like Fzrox