Joe said:2005-ish for me. At that time I was finally old enough to appreciate the park, but I was young enough to still be awed by that "something new at every turn" feel. At this point, the park was, in my opinion, still in its prime; AB owned the park, Le Mans was still in existence, Big Bad Wolf was still alive. No financial issues, the theme was still 100 times better than what we have now. I think, up until 2006 (maybe even later; I still don't mind Griffon very much) the park really was in its prime; it had finally found its perfect niche, at least as far as I'm concerned.
At that time, the park was doing what it did best: combining world-class thrills with natural beauty, lore, and wonder, with the latter taking the lead. It was at this time that HOS was experiencing its best years, Killarney was open and in full swing, and we had two truly awe-inspiring B&M legends gracing new areas of the park. I typically don't look at parks from a rides standpoint alone, but at this point I think the park had the perfect balance of rides and atmosphere. You could go to the park, ride a ride, play with dragons in a treehouse, do the Chicken Dance with a German dancer, eat one of those magical big pickles, or just sit and take it all in. Nowadays I bet almost everyone outside of this site goes to BGW with riding rides as their main reason.
So, I would take BGW back to where it was in 2005 because that's where my memories of the /perfect/ park are.