The best kind is the kind they use. I have four trays around the house, one upstairs for night-time peepee, one by the front door where they tend to spray if no tray is provided, one by the back door for the girls to poo in and another in the front room where we've had numerous "accidents" in the pist.
The upstairs one is simply a small kitten sized pink tray with a newspaper folded in the bottom, as is the front door one, but the two main trays are large deep open trays with clip-on edges around the top which helps to rebound some of the chucked about litter back into the tray.
I still stand all my trays on newspaper as some of them are rubbish at aiming. Polly actually stands on the edges of the tray and pees over the side
Our favourite litter is World's Best, expensive but it just seems logical to have organic litter for organic waste. I flush their poo down the loo but choose to bin the clumped pee, lest it block my plumbing
I'm trialling a new one at the moment called Sanicat Professional Gold, the pees come out like concrete blocks and it sticks to the scoop, nor is it flushable and it tracks everywhere, so I won't be buying this one again.