I just asked a similar question a short while ago. I hope the answer will help you too. But I had a few more questions reguarding the matter that may help you as well.
Here's the link:
https://answersrip.com/question/index?qid=20081111182639AA5VRxc
Here's the answer:
(thanks superj300)
If you have a business registered with an EIN, use the EIN for everything. Part of the purpose and benefit of incorporating is to prevent personal liability in the event of legal or financial troubles, and using your SSN when you have an EIN is not only incorrect, but may make you legally liable if anything goes sour. Think about it like this....if you owned a company with 30 employees that were all paid through the company, would you use your SSN or EIN on your 941s and whatnot? Of course you'd use your EIN, and the same goes in this case. A W-9 doesn't get reported to the IRS; the broker will hold it and use whatever name, address, and TIN you put on it to report whatever they are reporting on your 1099....non employee compensation, I'm assuming, unless this is an investment. Whatever TIN you put on the W-9 is where the 1099 will go to come tax time, so if you don't want to be personally liable for whatever income indicated on the 1099, you should put your EIN on the W-9.
To the issue of what tax form to use. Multi-member LLCs will file a 1065 "partnership" return with the IRS. Then, the K-1 that is generated by this return gets reported on your personal return. NEVER file a 1040 as multi member LLC. Single member is fine on your 1040, although again it raises the issue of liability, but multi member should definitely be on a 1065.
If I could offer one further piece of tax advice, you may want to look into filing S-elections in your state and with the IRS. Being an S-corp has additional tax advantages that may be worth it depending on your income levels and whatnot. However, remaining an LLC may also be beneficial depending on your state. In NJ, for example, two-member LLCs avoid some of the corporate business taxes that S-corps are required to pay regardless of income. A competent CPA firm can analyze your books and advise you on what entity is most beneficial to your situation.