Which robot kit is the most educational?

I want to start building robots, but I want to know which kit will grant me with the best learning experience. I was going to buy the Arobot (from Arrick’s Robots), but it states that the estimated time of completion is only 3 hours. I don’t think I can learn much in 3 hours. I have the money to buy multiple robots, but I need to know which ones I will learn most from.

this link should help http://roborobert.com/2007/12/5-robotics-kits-to-get-you-started.html