It really depends on what type of grass/lawn look you're after and what distance you're rendering at.  Here's a few examples.  If you're going to use EcoGrass, you should get Linda's Lush Grass and Lush High Grasses over at C3D.  The basic Vue grass plant blows.  Also, on the EcoGrass, you should use some sort of procedural or texture map base for the ground plane under the eco.