Considering the vast array of mountain bike disciplines and the diversity of rider preferences, what chainring size would be optimal for a mountain bike if the goal is to maximize efficiency and versatility across various terrain types, and how would this ideal size be influenced by factors such as crank length, cassette range, and rider strength? Would a smaller chainring size be more beneficial for technical, low-speed trails, or would a larger size be more suitable for smoother, high-speed descents? How would the ideal chainring size change if the bike is intended for cross-country, enduro, or downhill riding, and what role would the type of pedaling style and rider fitness level play in determining the optimal chainring size?