Formal:
* 我哥哥 (ngo5 gung1 ge1) - This is the most common and formal way to say "my older brother".
* 我弟弟 (ngo5 dai6 di1) - This is the formal way to say "my younger brother".
Informal:
* 阿哥 (aa3 go1) - This is a more informal and casual way to refer to your older brother.
* 細佬 (sai3 lou5) - This is a more informal and casual way to refer to your younger brother.
* 哥哥仔 (gung1 ge1 zai2) - This is a cute and affectionate way to say "little brother" and is usually used for younger brothers.
Other options:
* 我嘅兄弟 (ngo5 ge3 hung1 dai6) - This literally means "my brother" and can be used in a more general sense to refer to any brother.
* 我嘅親人 (ngo5 ge3 can1 jan4) - This means "my relative" and could be used to refer to your brother in a broader sense.
The best way to choose the right phrase depends on the context of the conversation and your relationship with your brother. If you are speaking to someone you don't know well, it is best to use the formal terms. If you are speaking to someone you know well, you can use the more informal terms.