I've had dogs, cats, birds, fish, and various rodents over the years so I have just a few words of advice: Get a CAT.
Let me tell you why you shouldn't get any of the other pats you mentioned. We'll start with dogs. Dogs require too much attention. You have to walk them at least twice a day or they'll shit and piss in your house. Plus dogs are pack animals which means they need constant attention and reassurance from the rest of the pack...meaning you...so if you have only one, they tend to get lonely during the day and start destroying things around your house until you return home. They also require grooming on a fairly regular basis or they start to smell worse than your dirty laundry. Oh, and vet bills.
Birds are just annoying and useless. They are also messy and prone to rare diseases and mites. They also are capable of flight so if you let them out they just shit and piss in places you'd never even think to clean. They don't love you, they don't understand you, they probably don't even like you, they just tolerate you because you feed them.
Rodents are like birds except they can't fly and they are even more useless.
Fish are like rodents but more useless still. Fish do have one redeeming quality though, you can flush them down the toilet when they die...try that with a guinea pig, or a parrot, or a German Shepherd.
Back to the cat. I've had many cats as pets over the years. They are affectionate, they are very low maintenance, they are self cleaning (seriously, I've owned many cats and never washed a single one-flea baths don't count, I think I still have scars from that incident though). As for fleas, thankfully there is a miracle drug called Advantage you just put on the cat once a month and you can avoid bathing your cat forever.
The single best reason to own a cat is you can lead a pretty normal life and not have to constantly be worrying about what they may be doing while you aren't there. You can even go away for a few days and just leave them a large bowl of food, plenty of water, and a clean litter box and they'll be fine. Can't do that with a dog.