I disagree with rainbow dash
I can't list them, I think TS is the smartest of 6 but she owes it to her friends right? And come on... how people can say that RD is dumb. She is the most practical pony ever - sleeples in Ponyville, hurricane Fluttershy (she is not so stubborn and knows where the line is... similarly in the episode where Scootaloo took offense at her friends. Dash knows what to say subtly and how not to press her) idk - the end in friend - she showed so many times she's cunning and resourceful. She impressed me especially in the episode about the wonderbolts' academy... And I agree that she doesn't like to think too much but it doesn't mean she's stupid. It's the only way to be like her. Think lazily and not too much. It seems to me that if she allowed herself to think more, she would be very helpless and lost. She just prefers to act than whimper like others. If we are to judge her by knowledge, then yes. She's maybe stupid in this part. But she is certainly not unintelligent or valueless. Her light spirit gives her a lot of lovers and haters at the same time.