For Madison, who lives in my room, I use a wood pellet cat litter, (says on the front is also safe for rabbits) and I've never had a problem with it - Maddie likes to use it and it's not messy, also, we can use the same litter for the kitten and Maddie.
Pebble and Ebony, who are living outside, have kiln dried pine shavings (safe), I tried them on the wood pellets too, but they didn't like them and just peed outside the litter trays. :?