Formal:
* Michał (pronounced "Mee-haw") - This is the most common and widely recognized Polish name, equivalent to Michael in English.
Informal:
* Michałek (pronounced "Mee-haw-lek") - This is a diminutive of Michał, often used as a nickname.
* Mikołaj (pronounced "Mee-koh-wuy") - This is the Polish equivalent of Nicholas, and while not directly related to Mike, it shares a similar sound.
Other:
* You could also simply use "Mike" as it is, as many Polish people are familiar with English names.
Ultimately, the best way to write "Mike" in Polish depends on the specific situation and your desired level of formality.