Specific recommendations are off-topic, so I'll answer generally (your question will likely be closed unless you generalize it more).
Those goals are diametrically opposed. So which do you want more - low risk or high reward?
In general, the riskier the investment, the more investors want to be compensated for taking that risk, so the more return they expect. Conversely, the safer an investment, the more return investors are willing to give up. So individual investors generally find a level of risk that they are comfortable with, and find investments that give them the highest returns with that level of risk.
Diversification also lowers risk (but reduces reward), so investing in multiple things (not necessarily the one "best") can be effective as well. Index funds do this for you. But even index funds have various levels of risk and reward.
If you want the highest expected reward per unit of risk, then one measure to look at is the Sharpe Ratio. It's the ratio of expected market return (above risk-free) to the standard deviation of returns (risk). Some brokers will publish a number for you. which is handy. If they don't, then it's either up o you to calculate it (which is tedious but not hard) or to use other measures. Morningstar, for example, has sliders for both risk and return for many mutual funds. You can fairly easily compare two funds to see if one has a higher return, lower risk, or both.
Finally, if you have any debt to pay off, then you could look at paying off the debt as risk free return, since you save the interest rate going forward with no risk of it changing. So that is often the best trade-off of risk and reward that you can find, especially if you are risk-averse.