Formal:
* Bom dia, amigos! (This is the most common and neutral way to say it)
Informal:
* Olá, amigos! (This is a more casual greeting, similar to "hello friends!")
* Bom dia, galera! (This is a very informal and colloquial way to say it, often used among young people or friends)
Regional variations:
* In Brazil, people often use "Bom dia, pessoal!" which means "good morning, everyone!"
* In Portugal, it's more common to use "Bom dia, camaradas!" which means "good morning, comrades!"
The best choice will depend on the context and your relationship with the people you are greeting.