Sand is by far the easiest when planting. I personally have the Seachem Fluorite gravel, with sand on the bottom.
Many other people on here love ADA Aquasoil, which is by far the best for plants, but degrades over time and leaves dust. For this reason, I chose the Flourite gravel.
It is really personal preference of what you think looks best. I would just look at a ton of pictures on here, or on Google and determine what you like best.