I use a combination of Citadel, Armory, and Reaper acrylic paints for the majority of my work.

Acrylics craft paints such as FolkArt, Apple Barrel, and Ceramcoat,  have cheap prices and handy flip-top bottles make them attractive, but don't use this sort of paint except for terrain. (Hint: for bases and terrain pieces, match your Goblin Green, Shadow Grey, and so forth with a craft paint color; it's a fraction of the price of using Citadel or other hobby paints.) They have a high ratio of binders and fillers to pigment, and turn into a grainy mess when they are thin down to a  working consistency;  layering and blending with them can be tricky. However, they mix well with other paints, and can certainly be used straight for base coats and such.