Do Robos or ETFs give higher returns long term?

There's no definite answer, as most robos ARE made up of ETFs. And they usually have multiple etfs stacked to beat the market performance. There are many different types of etfs in the market though. However, for which has the least fees, etfs would generally be cheaper most of the time, as there will only be 1 layer of fees.

Before your question, you should ask yourself whether will you be understanding the ETF you are buying and your constructed ETF portfolio make sense?

If not, then you should go to Robo as they choose the ETF for you and react accordingly to market.

If you are putting effort to read, build and manage your ETF portfolio, then there is chance your return will be better.