Eco Fuels

Have been considering using alternative sources, more sustainable ones hopefully, for some household heating. I've known about 'Eco Logs" for a while (made from compressed, waste sawdust), but recently came across a couple of alternatives:

1) Hemp logs - link

2) Straw logs - link

3) Leaf logs - link

I guess I'll have to try them all to see how good each alternative is (and how the eco-nomics work out). My gut tells me that the Eco (sawdust), Straw or Leaf should be better overall than the hemp, mainly because they are made from waste products rather than grown as a crop as hemp is. Any comments or opinions on the environmental impacts of each would be most welcome.