Well, it's different for everyone, but these are the pros and cons for me:
CONS:
Expensive. You have to buy good pellets, fresh veggies, bedding, hay, food bowl, water bowl, stored money for potential vet visit hidies etc...
Time consuming. I spend almost half an hour a day with cage cleaning, another half an hour for hand feeding, and several hours throughout the week with cuddle time.
The occasional poop or pee on your lap/sofa/chair/floor/personal item
PROS:
My piggy taught me to eat healthy
Having a piggy teaches patience
(the piggies) Lifetime of cuddles
Contentment in the fact that you are taking care of a happy animal
In order of difficulty of care, I'd say:
Horse
Dog
Cat
Chicken (I know it's weird to put this in the list but I have chickens)
Rabbit
Guinea pig
Fish (I'm putting fish before hamster because the water is hard to maintain)
Hamster
I know a lot of people say "piggies aren't and easier to care for than dogs", but I'm really not seeing it. I give my piggy personal time, feed him a wide variety of veggies, clean his cage daily (he lives in a 2x6 grid C&C cage), bring him into the vet for a checkup yearly, and a lot of other routine things. BUT, a dog is so much more work! You have to give them plenty of exercise or they become hyper, you have to bring them outside several times a day to do their business, you have to feed them a great quality diet, you have to train them constantly, and you have to spend huge amounts of time with them. I'm not saying it isn't worth it to have a dog, but dogs are in fact a lot more work than piggies.
I love my piggy. He's awesome, but he doesn't give me affection the way cats or dogs do. If I sit really still with veggies in my hand, he walks right up to me and eats. If I don't have veggies, he interrogates my hand insisting that I must be hiding them in a marsupial-like pouch. He'll sit next to me and fall asleep while I'm using the computer or doing homework, and just generally be awesome.