It really depends on what you ask for from a pet:
CATS:
cats can be known for being smelly and stinking a house up.
They like to sharpen their claws (Usually on your lap as you stroke them).
They are Independant animals, they like to roam where they choose and do what they want to do when they feel they want to do it. (Be prepared for certain cats just to turn their nose up at you and snootily walk off like they own the world)
Cat food reaks, and cats tend to nibble when they are hungry and walk off and leave it so they can come back to it later. (This can induce flys to land upon it, and can cause worming problems)
Cats hate worming tablets (They aren't like dogs where you can just put he pill in a slice of bread and watch it get wolfed down.)
Cats can be fussy when it comes to food, if they don't want to eat it they wont... but expect alot of presents turning up on your doorstep (Usually Mauled Voles)
You can't take a cat for a walk, without someone laughing at you. (Stupid people, can't take you cat for walk because of them)
Flee collars seem a good idea, but if your cat starts roaming around trees it might be possible that it could hang itself, as it has been known for a cat to fall and get the collar caught on a branch. (velcro ones release)
Cats hate Vets... So wear gloves when handling them (because believe me they know where your taking them) and make sure you have a decent sized transport container designed for containing a cat. (Not a Laundry basket like we use to use, as they sneak out the top and run round the car as your driving along)
DOGS:
In there youth they can be very destructive as a puppy, so your best trying to train them. Otherwise you might find a teatowel being chewed, along with shoes or even skirting boards. (Don't shut them in cupboards or they will just scratch at the door, and it does cause psychological trauma to them)
Dog food is smelly, and Dogs are renound for not leaving any for later. What ever you do, only feed them a meal or they will just eat everything until they are sick. (Some dogs don't like to be approached while eating)
Dogs do make alot of mess when they use the loo, and in recent years laws have been brought forwards to ask you the owner to clean up after your pet. (Plastic bags inverted are useful, just have your hand in the bag, grab the poop and pull the bag over it, viola place it in a poop bin. If it's runny inform you vet.)
If you need to give a dog a pill, just place it in some bread and give it to them, only on occasion will some dogs eat the bread and spit the pill up (How they manage that is a feat in itself)
If you have a car and intend to allow the dog into it, make sure you get the right equipment to enclose them in the back, so they don't disturb your driving. remember also to keep a lead on them, and tether them in the back also, that way when you open a door or the rear of the car they wont just run out.
When walking a dog, they can be silly when they meet other dogs or something they aren't sure about. Be prepared and put them on a lead if you see another dog walker.
(Sometimes dogs can fear heights and structures that they feel are unstable, like wooden walkways and bridges. Even horses and cows can make your dog cower)
If you have a dog, make sure you exercise them as they get really highly strung if they are kept in a house. If kept in a house then every visitor might be lept upon or a bite taken at.
OVERALL
Cats are cheaper, Dogs are in more need of Companionship. If your after exercise get a Dog, if you in the suburbs, then you probably already know that they are suited to Cats. (Please note that CATS are Terratorial, and if you get a cat for your area, it might have a few fights with other loal cats.)
Make sure you deal with reproductive issues, unless your after a litter of iligitiment puppies/kittens (If a Cat/Dog is female.)
Male Cats and Dogs tend to need to get the chop... To lower there Aggressiveness and other attitudes. (dogs are renound for jumping on peoples legs and cushions, and cats for Spraying)
If that's all too much for you, get a budgie or a fish, or some little furry creature or a snake.
Pet rocks don't need feeding
