Dogs, definitely.
Where cats are lazy and just sit around all day eating and pooping dogs actually make good companions, when I get home from school my dog always rushes to me, so at least I'm always greeted when I get home. Sometimes I am awaken by the cries of my dog when she wants to get up in my bed, but can't, reasons explained below.
I'm not really lucky with my dogs though, I've had two dogs, a male, who was tragically hit by a car after running away from home, and a female who has had a spinal hernia, which means she lost most of the use of her muscles on her hind legs, she's making a good recovery though.
I'm pretty sure even if I had cats as pets while growing up I'd still prefer dogs because overall I just prefer dogs' nature over cats', cats are lazy, dogs are active.
Maybe if I get another pet it'll be a cat, though a hamster is way up on the list. I have a feeling my dog would get along just fine with a cat.