I assume you're going for sand or gravel for cost reasons. Of course eco-complete, flourite, onyx...are all better, but cost more.
I've never used sand or plain gravel, but as far as what I read, I really have never heard anyone having any problems with sand. It better for roots then larger gravel too. Whatever you go with, root tabs and laterite would be good additives, especially if there will be root feeding plants.