I assume you ask because you are thinking of getting a large parrot. There is an order to the decision process...first, you must be sure that you want the bird, then be sure you are ready for the bird, and only then pick the bird. Getting a big bird is like having a baby. Actually it's like having a two year old child for fifty years. You can't let them out of your sight unsupervised, they will eat anything they find, chew extension cords, chew the furniture and woodwork, have tantrums, require special diets, require a LOT of attention, freak out when you leave them with someone else, not be able to tell you when they hurt or are sick, and require regular checkups and expensive medical care when sick. One difference between a child and a parrot is the parrot has a much more painful bite!
So the first step is to be sure you have the time to devote to this intelligent animal, the money to afford proper cage, toys an medical care, the living environment to tolerate loud noise and mess, and the life stability to make a long term commitment. Parrots live a long time, and they are intelligent. It's cruel to isolate a parrot or keep it in a cage without something to do. They can't be trained to accept human rules the way a dog or cat can be trained. They are traumatized when they have to go to a new home with new people.
Once you are very 110% sure you are ready, then read about the different species. If you read the individual forums here you will get a good sense of how they act and what kind of problems people ask about. You want to be sure of a good fit, because you will have the bird for a long time.
I encourage you, once you have done the above, to consider adopting a bird in need of a home. Good birds wind up in rescues or in need of new homes because their human got married, had a baby, moved to a different country, lost a job, developed an allergy...these birds may have emotional issues or treatable health problems, but in time will come to love you even more than their original owner because you saved them and somehow they know it. Most birds go through a very difficult puberty stage, and if you get an older bird it will have already been through that. You will get a good idea of the personality, know if it talks, etc.. Which are all unknowns in a young bird.
I hope you will stay around the forum a while to read about parrots and ask any questions. Don't be put off by my tone, please. If I seem discouraging it's because I have seen too many cases where birds suffered because they became inconvenient for an unprepared human, and because I know how intelligent and aware they are. You wouldn't get married or have kids on a whim and getting a parrot is the same type of commitment.