I dont know that 'smartness' can really be compared along a single metric. Different animals have different modules of intelligence and creativity in which their evolutionary line has expanded into. For example, monkeys have much more social intelligence, whereas dogs have more olfactory intelligence.<br />
As for spider monkeys? they're randy little buggers, avoid them
If I recall correctly, Michael Jackson had a chimpanzee named Bonzo or Bongo or something. Anyway, once it matured he had to give it to a zoo or something because it started doing that whole "alpha male" thing. <br />
The thing is, some animals are domesticated and some are not. Cats and dogs are domesticated. Spider monkeys ... I dunno. I'm sure you can BUY them, but will they be happy in that setting?<br />
My dog is sitting under my desk snoring contentedly. Our cat is in the other room snoozing in the sun. No other primates are in this house, apart from me and my wife.
I don't know which one is smarter, but the Dog is more Intuitive. And, will protect you, the Monkey doesn't care what you think, as long as you give it a Treat, and never hurt it. The Ape is more like a Crow Magnum, they protect their own kind, I think!