Reason 1 : Smell
when a dog smells, it smells bad
when a cat smells, it smells like popcorn usually, since that's how they smell when they've licked themselves...
Reason 2 : Drool
Cat's do not drool, this is a good thing because it keeps your car clean, your hands dry, and your house free from slobber.
Reason 3 : Biting
Given a single scratching post, cats are happy to just chill out all day and occasionally scatch the provided post, dog's will chew up any **** they can find, shoes, remotes, ANYTHING, they're like chavs and car stereos, only instead of stealing it they chew on it.
Reason 4 : crapping
Cat crap is a damn sight easier to clean up than dog crap, and alot less common too, if a cat needs to evacuate the torpedo chambers, it'll meow like holy hell, run rings around your legs and do everything possible to say in no uncertain terms, "dude, open the door i gotta **** now", a dog does not, a dog thinks, "lol i'll **** right here", also, a dogs idea of wiping it's arse is to slap it's butt on the floor and drag its ass around, this ain't cool if you have carpets.
Reason 5 : Brain power.
Dogs are freaking dumb, seriously, dog lovers claim cats are lazy/dumb, but check it out, a guy throws a stick, a dogs like "yey i'll go get it", and brings it back, only to have it repeated like 30 times..
Throw a stick for a cat and the cat'll just look up at you with WTF eyes and give you a "Dude, you threw that ****, YOU go get it your damn self".
I rest my case.