No going past pencil and paper!
With schools increasing their use of online software such as iNZight to whip up scatter plots and box & whisker graphs, or Desmos to graph equations, it still remains beneficial to take some time to reconstruct the process from the start with a simple data set or group of similar equations.
I really love the use of technology to learn maths concepts but there is no going past a pencil and paper calculation to formulate basic concepts and maths perspectives.
The answer is a combination of teaching and learning techniques, not one over the other.