Wacom proper size for a 24'' monitor

I work as an illustrator, and the 99% of my work is pure vector. A medium size wacom bamboo is my tool but know is dead and i need a replacement.

Acualy I use it, as a mouse since i work only vectors and the pressure features is not usefull in my field.

my monitor size is 24" and i dont know what to choose: Small or Medium.