i have had 3 chinese visas in past 2 years ( first - tourist second. 3rd 3 month M type)

In your situation, you should apply for a M type. You should ask any of these two companies to issue an invitation letter to you. Sometimes, the embassy requires the invitation letter from duly authorized Chinese unit. You'd better ask your factory to apply one for you from local foreign affairs bureau. Then you can apply for M type with your passport, application form, a recent passport photo, the invitation letter from the factory and invitation letter from duly authorized Chinese unit. Considering of your previous records, you may try to apply for a multiple one.