Series diodes won't regulate very well at all, and a 7805 isn't going to handle 2A. Any 'linear' regulator (series diode or regulator) is going to need to dispose of 14+ watts of heat anyways, which wastes more than you use.
A switching regulator is not as simple as a 'linear', but saves a lot of power. If you use the Black regulator, pay special attention to the current rating. Most of the designs on his pages are for 300mA and less, so you have to be aware and scale your implementation to handle the 2A that you need.