As said there are several 'best' substrates for snake enclosures. It all depends on what you define best as. The best for hygiene and cleanliness is newspaper, paper towel, butchers paper, etc. None of these though look particularly appealing and can be annoying to clean. If best to you is something more natural looking, coco peat, leaf litter (what I mainly use), different mulches, aspen and mixes are the better options. Some people find using kritters krumble (the paper pellets) is best as they like the ease of cleaning with it. Others swear by fake grass. For the most part its all pretty subjective. Every substrate has positives and negatives, best advice is do some research into all the different substrates and use what you think is best.
Personally I rather using more natural looking substrates. Currently I mainly use coco peat with a layer of leaf litter across the top. To me it looks the best, along with providing excellent stimulation for the snakes. In the future I will probably look into using different mixes and experimenting with what I find best and what best suits the animals I'm using it for.
Cheers, Cameron.