I would say negative.
It is positive.
Stubborn has a fairly negative connotation, implying that someone is 'stubborn' to the point of not listening to good advice, but since being stubborn can be a good thing under some circumstances,...
Both. All adjectives can be interpreted in opposing ways. Obstinate could be negative; 'stubborn', or positive; 'courage of your convictions.
it has a negative connotation, i believe
How to Navigate Office Politics
Adolescents on Positive and Negative Attitudes
Turning Negative Thinking into a Positive Outlook
How to Use Positive and Negative Space