I think the start of the Ignition Saga in 2006 was the best, because the sets started to look much better and the story got more serious, but the next years, set-wise, we're just getting worse (with he exception of 2007 sets), because the parts from 2006/2007 were just repeated and weren't very original, unlike the sets from previous years, which were fresh every year as the story moved on. Story-wise, Ignition Saga is the best in my opinion.