I've only used The Army Painter's Swamp Tufts, which I used on my Black Templars which I wanted to finish to a high standard. They are very cheap (mine cost £4, I think), and you get absolutely loads, I used 1 on each base for about 40 Space Marines, and I still have half the packet left.
My one recommendation is that you shouldn't rely on the sticky bottoms the tufts have, although they will stick fine on a bare base, if you are sticking them onto sand or another material add a dollop of superglue to the bottom of them. I think only 2 or 3 have fallen off after extensive gaming use, and I have simply applied some more glue and stuck them back on - no harm done. Overall I would highly recommend them, they shoudl have at least one variant to suit you as they have quite a bit of variety, they also look incredibly realistic for very little effort.
