I prefer Hero Factory over Bionicle. Bionicle's complex storyline, while it was great, was the reason why I gained and lost interest in the theme. The sets were great, but certain parts were hard for me to MOC with, and they broke alot. Hero Factory's simple storyline has my fullest attention, mainly since they're episodic. I'm personally in love with the HF Ball-and-Socket system, the stronger sockets that don't break makes MOCing with fun for me (instead of a chore of looking for a certain piece which isn't broken and unusable), and HF don't have many specialized parts, which makes using the parts simpler.