I like cats because they're reserved, and mostly quiet. Sydney usually likes attention, though, and meows at you whenever you say something to her.
Oh, and they are playful. At least, mine are.
A friend of mine has a big dog (I'm not sure about what type it is, it might be a Siberian Husky) who enjoys playing rough. I've seen him come to school with scratches on his arms, stating that he got them from fighting with his dog, Juno. He invited me to his birthday party and I saw him with a band-aid on his face. His dog had apparently made a gash on the left side of his face the night before his 14th birthday (yes, he's 4 years younger than me). He had to get stitches, and the band-aid was used to hide them from people. In the days we had school, the band-aid would've usually fallen off by the afternoon, exposing his stitches to everyone. They were removed after about 2 weeks, but a scar is there, and it still hurts him if you touch it.
'Nother reason why I prefer cats over dogs: Dogs're rough.