I found Bio-Catolet (paper-based) to be by far the most absorbent and therefore the cheapest and longest-lasting, but unfortunately it trails everywhere and my kittens are particularly fond of playing in the litter tray! So now I use the Pets at Home wood pellets which don't trail at all and are also very cheap, but unfortunately I get through it very quickly because it completely disintegrates as soon as it gets wet. The wood pellets have a pine scent which can smell a bit like urine but it isn't too bad, whereas the paper-based stuff seems to be very good at absorbing odours.

I use the pets at home wood pellets. Have not noticed any smell. In fact the woody smell is quite nice.