I used clay ultra-clumping for a while but find it heavy and not very effective. I started using Cats Best OKO clumping around 6 months ago and would never use anything else. It clumps really well so easy to get the soiled litter out. Weighs a fraction of clay. Easy and bio-friendly compared to clay. They say it can be flushed but it can block the toilet. It is easy to bag & bin although at the moment, I throw soiled litter on our wood burner.
It is really cost effective an I would say one bag lasts around 6 weeks (for one tray)
I would never go back to clay - so much so that I have 1 1/2 unused containers of clean n easy that I am planning to dump as I hate using it so much. I bought it a while ago when PAH were out of stock of Cats Best and it was BOGOF but I wish I hadn't bothered.
There are also health issues with ultra clumping clay
http://www.thelighthouseonline.com/articles/clump.html http://www.care2.com/greenliving/the-dangers-of-clumping-cat-litter.html- just some of the many articles about it.
If you look on Zooplus, it gets 5 star reviews (including one from me)
Some does end up on the floor but I find it easy to sweep up as it is light, whereas clumping clay litter when wet is disgusting and sticks to everything (like any wet clay)
I would say Cats Best Oko is the best ever cat product I have tried