Most people will void answering this as to give a definitive answer one must have certain qualifications. However as general information – if you contact one of the industry funds, they will take you through the set up from start to finish.
If under 19, In general you can just give your employee a choice of funds form, and they will either give u their previous/existing superannuation details or they can nominate a fund. It’s not your responsibility.
For ease of management, businesses with more than 20 employees may take a more hands on approach, but even having said that, this is often outsourced to an Accountant or Financial planner who has access to the many funds available.
There won’t be a significantly good or bad fund. Each fund has multiple investment options based on the client’s risk profile, and of course fees. The default is a conservative investment approach, but people who care about what their super is doing may opt into a more aggressive or defensive investment portfolio within the same fund. Returns differ of course, high risk high returns/losses. Low risk, low returns/losses.