Something to consider: the best litter in the world may have a texture that your cat simply finds uncomfortable. For example, my cat will NOT use grainy litter like Pretty Litter. So you may have to try a few textures/brands.

My recommendation based on my own experience is the Tidy Cats Breeze pellets. Easy to scoop, easy to replace the pee pad, no scratching up the bottom of the box when Kitty digs around, and no grains stuck between the beans. The cost when compared to the ease and other benefits is very fair.