I will highly appreciate to have your answer on my following questions

- I and my husband came to the US for studying since August 2005. Our visa are F1. Since then, we just left the US on vacations for 1 month and then came back to the US.

- We have 2 kids and one of them is American.

- My husband already finished studying since July 2007, and now worked full time job since August 2007, still on F1 visa .

- I already finished studying since December 2007 and now am looking for a job, still on F1 visa.

So,
1/ Are we resident or non resident for tax purpose? Which tax form should we file?

2/ Marriage jointly filling or separately filling, which way we will be better off?

Thank you so much

You will both file separate returns as nonresidents. On F1, you are exempt from residency for 5 years and you don't pay FICA taxes.

On your return you will get personal exemption of $3,400 and deduction as per tax treaty.
Read more about nonresident filing: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents