Both have their good qualities and their not so good. I've owned several dogs and several cats over the years. Dogs show their love and affection more than cats, but they are more trouble to look after. Cats are pretty well 'loners' but can still be devoted to their owners.
Incidentally, if you raise a cat and a dog together from kitty and puppy to adult stage, you'll find they become the best of friends. Yes, and one will miss and pine for the other if separated.
If you're happy to walk a dog every day - maybe twice a day, especially if it's a big or medium size dog, then dogs are great. If you're a bit of a couch potato, or find it hard to get much time to walk a dog, then get a cat. Both are excellent company.