Got $1000 to spare monthly: Mutual Fund or ETF?

I am finally in a position where I have an extra $1000 monthly. For a long-term view (5-10 years), which would be better to invest in? A Mutual Fund or an ETF?

I've already done a lot of research and at the conclusion of it all, it always states "it depends on you." So, I'm looking for more input from everyone to help me nail down my decision.

If it's a mutual fund, I'm looking at FIDELITY S&P 500 INDEX "P"; and VOO for ETF.