Is my pet legal?
First and foremost, find out which kinds of pets are illegal in your area. Don't ignore the laws (even archaic ones) just because you might get away with it; legal problems and heartache are a possible result. It is not worth the hassle.
Adult size
Larger pets need more space and exercise, and may be more difficult to handle. Will the pet still fit in your surroundings once it is fully grown? Do your research.
Sociability
Do you want a pet that enjoys human interaction and can be held, or a pet that is happier without regular handling?
Expense
Keep in mind that housing, supplies, food, veterinary care and other expenses are often far greater than the cost of the pet itself. Carefully consider what you can afford when choosing a pet.
Your long-term plans
If your life circumstances change (school, moves, marriage, children) will you still be able to care for your pet? Will it suit your lifestyle?
Veterinary care
It is a good idea to have a veterinarian lined up to care for your pet. For some of the more unusual ones it may be difficult to find one willing to see them, so see if you have access to vet care before choosing a pet.
Longevity
Some pets live a very long time and are essentially a life-long commitment (and some may easily outlive you).
Activity levels
Some pets are very active and require lots of exercise, others will be quieter (and some are so inactive they might be considered boring).
Destructive tendencies
Some pets are made to chew, dig and scratch, and require significant training and pet-proofing. And you thought a dog eating your shoes was bad?
Availability of pet sitters
Do you have someone who will look after your pet if you go away? Some of the more 'unique' pets may be a challenge when it comes to finding pet sitters. Not everyone loves snakes – as you are most likely well aware. Not everyone loves giant spiders. It's just not the same as looking after a fluffy small dog who is cuddly and cute.
Health concerns
Some animals carry diseases that can be transmitted to humans (the term is zoonotic diseases). This is a very important consideration if there are household members with vulnerable immune systems – young children, elderly people or immunocompromised people.
Potential danger from the pet
Some pets can be aggressive, dangerous or toxic. Really think twice about this one: why would you want to choose a pet in this category?