So I just went through this process about a month ago when I rebuilt my aquarium. Here were my findings:
ADA Aquasoil is the best option for growing plants, with Eco-Complete right behind it if you wanted an alternative brand. This substrate does lower the PH of your water for a few months. Pros are it has a ton of nutrients and very easy to plant in. Cons are it degrades over time and only last about two years. As it degrades it leaves dust on top and gets everywhere. It is also expensive.
Seachem Flourite is the second best option. It is clay based and comes in sand or gravel. It has some nutrients, but not much. Also comes in many colors and lasts forever. Also easy to plant in. Downside is it does not have nutrients, although it is said over time the gravel soaks up nutrients from the water. It also can be expensive.
Sand, and normal gravel is what many people use. Sand is extremely easy to plant in and looks really nice. Also pretty cheap. Downside is it does not have nutrients and fish waste just sits on the top. Gravel is also harder to plant in, which is what I used to have before I switched.
I personally went with the Seachm Flourite gravel (Dark) with Flourite sand as a bottom layer. I also put in root tabs and use PPS-Pro for fertilizer. I am happy with it. It all comes down to what you like as everyone has different opinions.
Whatever you do, make sure to wash the substrate (except the ADA Aquasoil) before you ever put it into the tank. I washed my Flourite gravel and sand for 2 hours everyday for a week and still did not get everything out. You will thank me later. Hope this helps!