Pretty much only wet food, except for a few kibbles every day because they love them so much, like treats. Dry food is super bad for cats, because they have very little natural thirst drive. This means they won't drink enough water by themselves, no matter how many fountains or water bowls you put out. This is easily explained. Cats are obligatory carnivores. This means that they need to eat meat. House cats are not different at all from their wild (and bigger) counterparts. Instinctively they do the same things. So ask yourself this: How do cats get most of their fluid intake in nature? Exactly! While eating their prey. Cats are 'used to' getting enough water by eating.

When you exclusively feed your cat dry food, they'll never get enough water intake to be healthy. This increases the risk of urinary tract infections and a bunch of other things. When you feed them bad quality dry food (lots of grains and non-meat filler), in addition to UTI's they will run a high risk of developing other problems like Diabetes.

So basically I'm saying: Only/mostly feed your cat wet food. The worst wet food is still always better than the best dry food. Because water is so important.

Edit: Also note that most of the "special diet" cat food is dry food. Which is ridiculous. I would never feed my cats that. Most vets have these well-known products like Hill's or Royal Canin that they prescribe.. PLEASE REMEMBER: Vets are sponsored by these brands, and pet food regulations aren't nearly as strong as they should be. Vets get money specifically for advertising and prescribing these brands. This does not necessarily mean that they are good for your cats. Why would a vet prescribe dry food for cats, when the worst dietary offenders are low water content and non-meat ingredients?