If my company wants me to contribute changes, who should sign the CA, me or my company?
The individual should sign the CA. If the contribution involves your company's property, then you need to obtain proper approval from your company. netbeans.org assumes that, when necessary, individuals have obtained the necessary permission from their company.
However, if there are many contributors from the same company it is impractical to send individual OCAs for each employee. In such case it's possible to send a blanket company OCA.