I chose the ScoopFree Sensitive Crystal Litter trays when I received the ScoopFree Litter box.  This is a game changer for me!  No more scooping every day.  The machine does the work and in a few weeks, I replace the filter with a new one.  That's it!  Since this was a new product for my kitty,  I went with the Sensitive Crystals first.  I will probably try all the scents at some point.  You are really going to love this setup!  Life just got a bit easier with this!