The bearing angle between two vectors?

What is the best way of showing the angle between two vectors defined by start and end points?

E.g., Vector 1 points from point A to point B. Vector 2 points from point C to point D.

I have tried:

$\angle (\vec{AB}, \vec{CD})$

But it is ugly.

In addition, the abovehead arrowhead is not long enough to cap the long expression. How may I fix this?

$\angle (\overrightarrow{AB}, \overrightarrow{CD})$
$\mathbf{a} = \vec{AB}$
$\mathbf{b} = \vec{CD}$
$\alpha = \angle (\mathbf{a}, \mathbf{b})$