* ζωή (zōē): This is the most common and general word for "life," referring to biological life, existence, or the living state. It's often the best choice unless you need a more specific meaning.
* βίος (bios): This word refers to "life" in the sense of a way of life, one's existence, or a biography. It emphasizes the lived experience rather than simply biological existence.
* αἰών (aiōn): This word signifies a "long period of time," an "age," or even "eternity." It can refer to life, but with a connotation of duration and perhaps even a cosmic or divine aspect.
The best word to use depends heavily on context. For most situations, ζωή (zōē) is the appropriate choice.