Which disorder is most easily diagnosed and characterized by pronounced mania?

Bipolar I disorder is most easily diagnosed and characterized by pronounced mania. This disorder is defined by the presence of at least one manic episode, which significantly impacts an individual's functioning. A manic episode is characterized by an elevated mood, increased energy, and often risky behaviors that can lead to negative consequences. The manic symptoms tend to be severe enough to warrant hospitalization to prevent harm to oneself or others, indicating a clear and dramatic presentation of the disorder.

In contrast, Bipolar II disorder involves at least one major depressive episode and at least one hypomanic episode, but not the full-blown manic episodes seen in Bipolar I. Major depressive disorder does not include the manic or hypomanic episodes at all, while disruptive mood dysregulation disorder is primarily characterized by persistent irritability and frequent temper outbursts, focusing on mood regulation difficulties rather than manic episodes. Therefore, the clear and marked mania associated with Bipolar I distinguishes it as the most straightforward diagnosis among the given options.