Because hey, we have to start somewhere. Even though the system isn't the key to a good RPG a good system certanly helps.
My personal favorite is the White Wolf system. The dotsystem is really simple to get, it's really easy to get an overview of your characters strengths and weaknessess, yet it's really balanced and corresponds to how the world works in a good way. Simple, yet well rounded.
So, what's your favorite system?