Whatever you do, don't buy the fragranced cat litter. I'm convinced it makes cats nauseous and causes them to dislike the box. When my cat was sick with cancer she became terrified of the box, and I now suspect the odor-eating stuff in the litter might have been making her nauseous when she smelled it.

Get litter that is 'fragrance free' and as chemical free as possible.

I now mix the fragrance-free litter 1/2 with plain cedar shavings litter. Seems to work for us.