I tend to use World War Scenics because they are cheap and have a decent variety of colors. Honestly I don't think grass tuft quality varies so much between brands to worry about finding the best one.
If you're just starting to do bases, I'd recommend popping by WalMart or somewhere equal and buying cheap craft paints (for the US Applebarrel paint brand). Use these to paint and drybrush your bases. No need to use expensive hobby paints for a dirty base.
Do drybrush if any of the texture area will be visible, even if the paste is already a good foundation color.
Other than tufts, if you are making bases as somewhere with foilage, I'd recommend getting flock. Woodland Scenics sell jugs of flock in different mixes. Get one that looks right. Apply PVA glue to the base and then dunk it in the flock and gently tap off the excess and let it dry.