Best, student friendly, graphing tool

Desmos is a beautiful, free, graphing tool that offers a tremendous flexibility. Students can use sliders to play and explore transformations of graphs.

The ability to imbed images allows my students to write equations to model the parabola formed by a water fountain. With Google sign in, my students can send me graphs they created.

A colleague had students build drawings from linear functions with restricted domains.

This is the best graphed I have found, and it is free.

Maharajah of Mathematics about Desmos Graphing Calculator