Am I considered a resident alien for tax purposes while on H1-B visa if I am present in the USA for1 year now? Should I fill form W-8BEN or W9 for income through equity?

Am I considered a resident alien for tax purposes while on an H1-B visa in the USA if I have been present in the USA for over 1 year as of Dec 6th 2015. I need to certify my tax with my Equity firm to avoid U.S. tax withholding of 28% which will deducted from the gross proceeds on failure to declare tax. I am not sure if I need to fill Form W9 or W8-BEN. Please advice.