Dogs require a lot of care and attention, whereas cats are very independent. You have to walk dogs twice a day, but cats can take care of themselves. Dogs often destroy furniture, and sometimes they can be violent and bite people. Cats do not harm anyone if they are left unprovoked.
I prefer cats they require less one on one time but are still cute and lovable when you need them. You can play with a cat and maybe throw some string around with it, but you can stop at any point. Dogs make it hard to stop playing because they will keep bring you the toy until you are crazy exhausted.
Dogs are loud, active, need to be walked and often start fights with other dogs or even people. They are harder to potty train, and often insist on going to the bathroom little by little everywhere so as to mark their territory. This can lead to droppings being in unfortunate places for people. Cats are far easier to potty train and typically don't need to be trained, so they are better for everyone overall.