Kittens are by far cuter. While both are cute, but if you startle a puppy it pees it self which can be inconvenient, also puppies have a tendency to come off more silly, clumsy, and clueless. The latter is still amazingly adorable. But kittens tend to come off more curious, personable, and their playfulness beats a puppies for cuteness.
People say adult cats are lazy and such. But really cats and kittens can be trained too, they're just on average much smarter, which makes them more aloof and stubborn. You can get a dog to do just about anything, and they're more useful in a lot of ways, but! Dogs are also basically helpless in a ton of situations and will always come to their person for help. Dogs also have more of a tendency to get neurotic if not properly entertained, trained and exercised. Cats on the other hand generally can take care of themselves on most things, if you always have food out for them they can learn to eat just enough to be satisfied, and only need help for a few things. Also cats are happy to be your companion and be there with you, dogs on the other hand are just plain needy. Both are good in their own ways, but having had lots of experience with both, I like the calmer and less needy nature of cats better.
Also yes cats are smarter, they have more than twice the number of neurons in their little brains. Dogs are still plenty smart, but the smarter the dog the more you need to exercise it, play with it, and... Well the smartest dogs are working dogs, and they really do need jobs. Plus dogs have very specific roles from selective breeding, so herding dogs will always try to herd things/people, just for example. Cats are more versatile for pure companion animals, because that and hunting pests is about all they're bread for. Cats are apex predators too so they tend to spend more time conserving energy. Dogs are part scavenger and mostly endurance hunter, so they like to spend energy. Mix that with the pack nature of dogs, they need to be run hard and know their place. Socially cats are more just groups of equals who hunt separately and then hang out together for mutual protection. Cats are just easier to handle for those reasons.