I’d suggest anyone who has a little budget to buy Quad Remesher. It’s simply the best auto-retopo algorithm and has never been superseded or even equaled (although I believe the recently added 3ds Max auto-retopo modifier is quite good as well, as is 3D-Coat’s Autopo).
Hobbyists can buy a Perpetual Indie non-commercial license for $ 59.90, and anyone who earns money using Blender can buy a Perpetual Pro license for $ 109.90. As someone who comes from the world of 3ds Max and its expensive plug-ins I can tell you that’s quite a bargain.