how to apply different numbers of attack animations in code for animation controller?

i'm using unity5.

basically i have many characters with different numbers of attack animations, most of them is 1, but can be as many as i want. every time the they attack, they will play the animation randomly(or in sequence).

currently i have a AnimationController with just one attack state, and i used a AnimationOverrideController to switch the animation every time the character attack, but it's difficult to determine when to switch the animation, and I must call the Animator.Rebind() method to apply it which takes a lot of CPU process time.

but to make more than one AnimationControllers is a bit silly, and it will maybe work for some time, but this is a absolute bad choice.

so i run out of ideas. the good old Animation component maybe a good choice, but that's a legacy system, in theory we must embrace the new mecanim system right?

anybody please give some thoughts? thanks!