Either will work or you could setup a soil based...I have a sticky at the top of this section on the soil based planted tanks or NPT's.
If you go with gravel-get small diameter and with sand don't go over 2 inches.
What is more important with successful planted tanks...Is the proper color temp light....Without the proper color temp for photosynthesis the plants won't grow as well or thrive. I use the Daylight 6500k florescent bulbs...color temp in the range of 5000-7000k with the ideal being 6500k color temp. With a photoperiod of at least 10h/day...
I'm so glad OldFish is here to help us with our plants :D Its really awesome having a planted tank especially since I don't have a yard, and therefore no garden, to grow plants in. The fish are always happier too!
I just switched from gravel to pool filter sand..Planning on getting java moss and Java ferns so it's more for looks than anything since I will be attaching them to driftwood and rocks but I love how it looks.
I tried to put my signature but the ink wouldn't go through my screen.