The very Definition of intelligence is a Problem here I think.
In fact cats have cunning and are more or less solitary, so the also distance themseleves from their pet human.
Dogs are well to Train and are herd animals, so they try to please their master (or bring them into Submission, as sometimes observed).
I would state it like this:
Cats have a very specific kind of intelligence. Within that limit they may well be more intelligent than dogs, but outside it they can't compete, nor can they expand their boundaries much.
Also, cats are much of a muchness. Some are cleverer than others, but rarely if ever to a great extent.
Dogs are generalists. They're not as clever as cats in catty areas, but much more intelligent in many others. What's more, most of them are more willing to learn not just new tricks, but whole new kinds of behaviour.
Also, dogs come in many kinds. Some are inherently lazy, fixated and slow to learn, almost catlike. Others are naturally curious and eager to do something new. The range of their intelligences is much wider than that of cats.
I prefer dogs, but own neither.