My vet's advice was as much meat as possible, no grains. Ignore anything about 'natural ingredients' if that means herbs and carrots or whatever - as she said, it's not as if cats naturally eat carrots, that's just on to appeal to the owner not the cat.
If the ingredients has a high ash content, that's bad.
Kittens need to eat kitten food wish vet would explain this to my kitten who just wants to eat old cat's urinary dry food
Taurine, omega oils, vitamins, pre and probiotics is good esp for senior cats (what I'm looking for)
I'm currently feeding Bozita wet and Sanabelle dry to the kittens who are v happy, and James Wellbeloved wet + vet urinary dry food to older cat who is less impressed. Hunt for her favourite food continues.
I love Zooplus for so many options for grain-free food, much cheaper than highstreet and all delivered to your door.