Basic strength of nitrogen
Tang Yong Boon certainly is in the correct direction (please refer to his comment).

I'll just wrap things up: 
$$\gamma &gt; \beta &gt; \alpha $$
$$\mathrm{(Basic \ strength)}$$

Reasoning: 


The $\gamma$ nitrogen is unquestionably the strongest basic site. 
$\beta$-nitrogen follows, as its tendancy of lone pair donation is greatly enhanced due to the presence of an adjacent (ie. alpha wrt. itself) electron donating group ($\ce{-NH2}$), otherwise known as the alpha effect. Some explainations include destabilization and elevated energy of the ground state, resulting in lower activation barrier.
The $\alpha$-nitrogen is best called an acidic site.