Is It Ohayo or Ohayou?

Ohayo (おはよう, ohayō) is a colloquial term meaning good morning in Japanese.

Is it ohayo or Ohayou Gozaimasu?

#1: Good Morning = Ohayō おはよう / Ohayō Gozaimasu おはようございます

This is the casual form, which you'd mainly use with close friends and family members. The second way to say good morning in Japanese is ohayō gozaimasu おはようございます. This is a more formal version.

How do you write Ohayou?

The greeting "Ohayou Gozaimasu" can be written in its hiragana character form (おはよう). This is a shortened way of saying good morning. For more formal situations, the longer greeting of (おはようございます) can be used. For reference, the longer a greeting is the more formal it will sound.