What you use will depend on personal preference, local climate, species you are growing, etc. Use whatever you would normally use in pots.
Just be aware that net pots dry out quicker than normal nursery pots so I'd be wary of really fast draining soils in your area unless you have lots of experience watering well. I don't have enough time/have not mastered watering these well enough through our dry summers so I get better growth in normal nursery pots that don't dry out as quick.
