Substrate is critical for a new planted tank, it is NOT a secondary concern. If all your plants are just anubias, java fern, and moss then yes you dont need a good substrate. But if you plan to grow any root plants at all such as sag, hairgrass etc.. having a special nutrient rich plant substrate at the get go will help tremendously.
There are no perfect substrate, below is the list:
Ada aquasoil: considers to be the best and near perfect, downside it will cause cloudy water and nitrate spike after initial setup
eco-complete: good nutrient rich substate, easy to plant and will not cloud water, downside it has the potential (depends on the shipment) to raise ph/gh, it will go away after a few weeks
flourite: never used this stuff, it's cheap. Downside is it's a mess to setup, and not as good as the previous 2.
If you have the cash go with ada, if not eco complete will work well too, just dont introduce fish to the tank until ph is stable.