SB was the best content wise because we still had HM dungeons, and we got Eureka (Yes I had my complaints at the time but I still did it and it at the very least gave me something to do). The extra Rathalos trial. I never felt like I was at a loss for what to do then. But I had started playing right before 3.4 dropped so maybe SB being my first expansion launch added to the magic.
Of course I am not taking the battle system into account because I do not feel like my understanding of it back then was good enough for me to know if I'd want to go back to it or not (I was also bouncing between different classes to main) so I don't have any nostalgia for it.