Eco complete may also be a good option. But my real suggestion is that you actually try the dirt tank.
Why? Because this is a new and empty tank. You don't need to rush it or be in a hurry to add fish. You have all the time in the world to research it, and do it properly, and allow it to cycle fully. And when you are done you will have learned something new and will have an excellent substrate for your plants.
If your not happy with that idea try eco complete, Mr aqua soil, or ada soil. All are good options and easy.