Should I pick a couple of all-in-one type ETFs and make regular contributions or put them in a portfolio with a robo-advisor?

Let's be honest: Robo-advisors are going to be investing into an ETF anyway.

ETFs, especially ones that track the major indexes, are typically the go-to investment choice for most investors. You are going to pay anywhere from 0.1% to 1% for something that you could do for free.

Why bother paying for a service to do what you are capable of doing yourself?

You are right in that ETFs are simple, so you are not missing anything. You are essentially investing in a portfolio of stocks that are passively managed by the investment house

When it comes to picking what ETFs to invest in, it depends on your objectives and savvy.

Do you want to invest in the S&P 500, for example? You can choose ETFs that mirror the composition of the index and then pick ones that have the best dividends, overall performance, and expense ratios.

If you want to park your money in a sector, you need to find ETFs that invest in energy, technology, entertainment, or bonds. You then use the same criteria: best dividends, overall performance, and expense ratios.