Formal:
* Maisha ni mema: This is the most literal translation and is the most formal way to say it.
* Maisha ni mazuri: This is similar to "mema" but emphasizes the beauty or pleasantness of life.
Informal:
* Haya maisha!: This is a more casual and affirmative way to say "life is good!" It literally translates to "These are the good things!"
* Sijutii kuwa hai!: This is more expressive and means "I don't regret being alive!"
* Nashukuru kwa maisha!: This is a grateful expression meaning "I am thankful for life!"
The best choice depends on the situation and your relationship with the person you are speaking to.