I had a cockatiel when I was a kid for several years until she died suddenly. :( She'd always been a bit of a "special needs" type bird in a way, she was a more clumsy than your average cockatiel and the lady we got her from gave her special attention because other birds would try to pick on her. I loved her, she was so sweet. She was loving, intelligent and very entertaining to watch and interact with. Birds can make wonderful companions (although some species like finches do not do well with handling), but I find there are drawbacks. For cockatiels in particular, they are prone to night frights, I believe they are the only species of bird commonly kept as pets to be prone to night terrors. If you have your cockatiel in your room (or in an area close to where you sleep) be prepared for the possibility of waking up during the night to a noisy screaming bird! Some birds can be very loud and/or destructive! It depends on both the species and the individual bird, I'd recommend getting a bird from a rescue so they will know more about the individual and its habits, noise and destructiveness level than a pet store generally would. petfinder.com is a great resource for finding a pet, they have many birds listed there! If you live in an apartment, you may not be allowed to have a bird due to noise. As stated before, a well cared for bird, depending on the species will live a long life, especially when compared to something like a betta. Some larger parrots like macaws can live over 80 years! Depending on your current age, the birds age, and how long its species lives, you may have to write your bird into your will as a young bird with a life span of a human will outlive you.
Another drawback is the cleaning. Birds are messy. They don't poop in just one place in the cage like a cat in a litter box would, and food like pellets,seeds and husks go about the cage bottom and even on the floor around the cage. Some birds seem to deliberately throw food, others are just messy when eating. The cage, perches, and toys all need to be cleaned. While many cages have a convenient pull out tray that makes the cage floor easier to clean, the "bar part" of the cage still has to be cleaned, as well as the bottom part that the tray slots into, and the wire grid (if there is one)that sits on the bottom, all of which can be more difficult to clean than the pull out tray. Many smaller cages have a detachable top piece, bigger parrot cages might not. Having a big sink to was and rinse the tray in helped. An appropriately sized cage depending on species can be expensive and may require more room then you actually have available. If you use any nonstick cook wear you cannot keep your bird in the kitchen, either keep it in another room, or get cookwear that is not nonstick.
Beware if you have cats! We had two cats at the time, both rescues- an old cat who had claws but never bothered the bird due to age, and a younger rescue who was declawed but who bothered the bird if she ever got the chance. We'd keep her closed out of my room at all times, but occasionally she'd sneak in without us seeing, or when we'd bring the bird in its cage down to the kitchen or living room to spend time with us there and give it a change of scenery, the cat would want to try bothering the bird! Like I said this cat had been declawed in the front, so couldn't scratch the bird and the bird would avoid the cat by just moving away but the few times it happened it still stressed the bird out. The bird learned to squawk for us if the cat snuck in and bothered her, and because of the cat not having front claws it couldn't really hurt the bird but it worried us a lot to think if the cat had gotten that door open somehow and was harassing the bird. If you have an older cat that stays on the ground you should be ok though.