Between the options mentioned below, which would maximize my returns in long term such as 10 years or so even more?

Don't plan to time the market. Stick to your risk profile and stay invested. Markets will go up and down, it's inevitable, but we only don't know when.

One thing that has been certain so far, is that even if you invest at the highest points before a crash in a globally diversified portfolio, but stay invested for a good 15-20+ years, you will still be in the green.

We've been expecting a crash since 2016. Hasn't happened. If you stayed defensive, you'd missed out huge gains in 2017. If you turned defensive at the end of last year, you'd miss out on one of the highest quarter YTD returns for the start of 2019.

Yes, I certainly agree with Gabriel and Hariz. Let me share with you my observation during the 2008 GFC.

During that period I was still in the sovereign wealth fund GIC. Investment professionals were split in opinions on whether a crisis is about to unfold. Even professionals with decades of experience cannot time the market, so I would really suggest individual investors not to fall for the disillusion of timing markets. We are just not as sharp as gurus like George Soros, unfortunately.

Secondly, many investment professionals were way pessimistic or conservative way too early. They held high allocations to cash and tend to miss the run-up.

When the crisis finally develop, they panic thinking it would be the end of world stock markets ("this time is different" phenomenon) and did not buy into the discount, thereby squandering away a precious market opportunity.

Therefore, in conclusion, its more discipline to maintain a consistent risk profile throughout. Astute investors would have always set aside emergency funds. If there are no foreseeable need for the emergency funds, you may utilise part of it to take advantage of market corrections that presents itself from time to time to improve your investment returns. Do replenish the utilised portion when you receive your subsequent months of wages though.

Set and forget. Advantage of robo advisor is you can set a plan, set your regular contributions, and forget. Really just go pursue your hobbies, do something else to occupy time.

You can check back in once every few months or even once a year. The less emotional ties you have with your investment the better, so there will not be any panic mode selling or euphoric buying.

Maximizing returns over 10 years will also depend on your risk profile that you have done for the robo sign up. Different risk levels will have different expected or projected returns. If you can take the maximum drawdown risk, you will also expect the maximum returns.