Silver

bronze is fun. Anything goes. Team comps don't matter and pub stompers (in my opinion) are fun champs to play. As you go up in ranked things get more rigid and people will punish poor decisions and bad team comps. Also the long games are fun and always give you a chance to come back instead of those silly games which are 20 minutes long because it is such a stomp in one direction or the other.

To be honest, my favorite rank is gold. It's where it becomes incredibly rare that your teammates play AD karthus, and most players are willing to put in some effort, but you are not punished that hard for your mistakes.