If you have very small kittens, you would need non clumping litter. Little ones tend to try to eat it and it can be harmful to them and cause blockages. I've used both but tend to prefer clumping.
I prefer clumping because it’s easier to clean and monitor. I know what the “typical” size of my cat’s urine ball should be and can notice if something looks unusual.
But, for kittens, larger non clumping pellets are usually safer until they get older.
Hi! Clumping clay litter is made with bentonite clay, which is dusty, not environmentally friendly to make or to dispose of and some believe that breathing the dust is harmful.
With all that, I'm using it because as others have mentioned I like the clumping, and I mix it with littermaid's walnut litter which the cat likes and that actually absorbs the dust.
I have never tried Dr elseys respiratory relief crystals, nonclumping I assume, but I know some members like it.
I LOVE clumping litter for all of the reasons listed above. It is easy to clean and typically less smell as you are able to scoop out the urine. Clumping litter also doesn’t need to be dumped every day week unless your cat is super finicky about his litter box.