H1B Extension Approved From March 2011 to March 2014.
I94 valid till March 2014
Given 3 weeks termination notice by my employer on 04/05/2011.
Assuming that my employer will terminate my H1B on my last day(04/29/2011)

What is the safer option(higher chances of approval) to stay in the US for a few more months within which i can look for a new employer??
Change of Status to B2 (Or) Change of Status to F1(Already have an I20 from a university)?

Do i have sufficient time to apply for Change of Status and still stay in the US while COS is pending and H1B is terminated??