I took Calc and Analytic Geometry 1, 2, and 3 in college. I thought Calc 2 was the toughest, and Calc 3 was the easiest. Then ended up never using it and can't remember any of it at all now. Its been around 10 years or so since I finished Calc 3. The only thing I remember was my instructer telling me after I was already taking 3 was that I should have taken differential equations after Calc 2 and before Calc 3. Something about differential equations uses alot of what you learn in Calc 2 and it was easier taking it after Calc 2 while everything was fresh in your mind. I ended up not even taking differential equations. Well I enrolled in it, but dropped it a couple weeks in when I stepped away from school to enjoy watching my son grow up.