The level of affection a cockatiel shows isn't primarily determined by its gender but rather by how it's raised and trained by its owner. When properly cared for, both male and female cockatiels can become very attached to their humans. Generally, female cockatiels do not whistle, so if you're interested in a whistling bird, a male would be the better option.
A cockatiel's tendency to be affectionate is not tied to its sex; it largely depends on the care and training provided. With the right approach, both male and female cockatiels can form strong bonds with their owners. It’s best to start with a young bird, as those raised by their mothers are often less likely to bond with humans later in life. During the early stages, hand-feed your young cockatiel and spend a lot of time with it to help it acclimate to human interaction. Avoid keeping your cockatiel caged all the time. Allow it to roam freely daily, and use food to encourage it to step onto your hand. This will strengthen the bond and increase its dependence on you. Cockatiels raised in this way, regardless of sex, will become very affectionate.
For a cockatiel to be affectionate, the key is hand-raising from a young age. Cockatiels are medium-sized parrots with quite a bit of feather dust, so regular bathing is necessary. If you specifically want a bird that can whistle, choosing a male is better since females typically don't whistle. You can teach a male cockatiel to whistle by starting to whistle tunes yourself. Once your cockatiel starts to call your name, it can learn to whistle and perform a few catchy melodies. The key to an affectionate cockatiel is proper handling and teaching, not its sex.