chinchillas live for a long time so you have to be certain that's the pet for you, gerbils are clean and don't smell but can easily fall out with each other if in a group larger than two, they are also active at every waking hour and amazing escape artists. Not a pet to have around cats they also don't form a bond with their human and aren't very cuddly. More of a watching pet. Degus and guinea pigs need a lot of space to run about in. And birds make terrible indoor pets as they need a large flight area to truly be happy. My perfect pet are my four rats they are incredibly cuddly especially the older ones, form a really strong bond with their owners, really clean and people who have them say they are like having mini dogs because they are so intellect. The only down side is that they don't live long and you will probably need the vets at some point as pet rats tend to be genetically weak unless you buy from a breeder. But I'd do lots of research if I were you
This is a good rat forum for learning about rats
http://www.ratztails.co.uk/supportforum/Blah.pl