Saya is a formal form. Aku/-ku is an informal form. Both means "I" (subject) or "mine" (object) Saya is used when you speak to older people or to strangers. To show your respect. for example: Oh iya pak, buku itu punya saya. (oh, yes sir, that book is mine). Aku is used when you speak to your friends (of the same age). for example: Hai! Kemarin aku lihat kamu di PTC. (hey yesterday I saw you at PTC)

Saya is formal, and Aku is informal. You use Saya to older people or someone you looked up upon, While "Aku" is to friends or people at your age

SAYA used when you are talking to older person or someone who is new for you. SAYA is for formal situation. you can use AKU when you have conversation with your best friend or someone who close with you. AKU is for informal situation.

Saya is more formal than Aku. Saya is used in formal settings, for example in an academic seminar or to older person. Aku is used in informal settings or to friends or close friends. Your close friends may differ in age,but if he/she is close to you, you mas use "Aku". But sometimes people feel that "Aku" creates distance. Some other people feel that "Saya" creates distance. But as long as your friend is okay with whatever you use, so be it. I suggest that you use the first paragraph for simplicity in use.

well, saya is a formal way to say "me" or "I am". it usually used to someone who's older than you or a person you who you've respected, or we also used it in a serious/formal situation. and aku is an informal way to say "me" or "I am". It usually used to older person too (but it usually used in family. to your mom/dad/uncle/aunty) *its a nicest way The slang one which usually being used by teenagers is "gue". but it really impolite if we used this to older people (even they're our family). They usually used it around their same age- friends or someone who's rrrrrrreally closed to them. Hope it help! :)