Cillian's 3 Best Performances
I'm not sure if the other topics that ask his best movies are for how good the movie is or his performance in them so this topic is strictly performance.
It'd be hard to choose just one out of all his amazing roles so for me I'd say:
1. Breakfast on Pluto
2. The Wind That Shakes The Barley
3. 28 Days Later
I've changed my minds many times.