If you have a choice, don't get a cat, get some kittens. Any number from 2 to 4 is a good choice.
Sometimes you want a mature cat, or just one cat or kitten, especially if you already have cats in the plural.
But over the lifespan, a litter of kittens is best. There's a special bond between cat siblings which, among other things, leads to a lot of perfectly adorable nuzzling and cooing amongst them. They're prettier as a matched set, a role they will happily perform in an infinite number of variations around the house for their entire lives. And believe me, you haven't really lived if you've never had four purring cats in your lap.
Maybe the most interesting thing, though, is being able to see the differences in their personalities so much more clearly with the side-by-side comparison of their siblings. In groups larger than three, cats don't rotate around their owners as strongly as one or two cats will, and tend more to their cat business, whatever that may be.
Get kittens. You'll thank me later.