I know it also really depends on the fighters in each weight class, but I have loved the light heavy division for quite some time now.
Even pre-JJ it was exciting as hell. Fighters with KO power that are much quicker and don't gas anywhere near as fast as the heavies.
What say you? 
Once the Strikeforce fighters went to the UFC, 185 has been petty damn fun to watch. I also like the 155ers. 