YOU SAID:
You are a great friend to me.
INTO JAPANESE
あなたは私の偉大な友人であります。
BACK INTO ENGLISH
You is a great friend of mine.
INTO JAPANESE
あなたは私の親友です。
BACK INTO ENGLISH
You are my best friend.
INTO JAPANESE
あなたは私の親友です。
BACK INTO ENGLISH
You are my best friend.
That didn't even make that much sense in English.