Used to like cats more, but dogs are my choice now.
I like how there's things to do with them. My cats are content to be inside, curled up on a chair, and sleeping for most of the day. But my dogs like getting out of the house. They like doing things, and in turn, that gets me up and doing things. Because of my dogs, I get outside and get exercise that I wouldn't have gotten otherwise. I also have a hobby (dog training) that gives me a reason to get out of the house. And there are a lot of places that I explored/want to explore that I wouldn't have otherwise only because I thought they would be a fun place to take my dog.
Plus, dogs are more affectionate in the way that I like. Right now, my oldest dog is under my feet. And both of my dogs bark and act so excited when I come home. It's a nice feeling to know that my presence is enjoyed that much by other living beings.
There's also the fact that dogs are less messy than cats. My two cats have made a mess of the room that they spend a lot of time in, and that's just from the litter dust alone.
I could go the rest of my life without another cat. But I know I want to have more dogs in the [far far] future.