According to this page at intel.com
there exists no P4 3.06E. The number 3.06 is only possible with a 533MHz FSB. So if anybody is selling that, it is most likely a "typo". Or more commonly: The people maintaining the sellers website don't know nothing about hardware.
Your question is: "Which chip is better for me A or A+?" And then you don't tell us more about your needs to base arguments on. Tell us what you need it for and what your requirements are, then we can give you advice. As an aside, I can hardly find an argument to advise anybody to buy a P4 Prescott over an AMD64 for a silent computer at the moment.