What is the best editor?

As stated above. If you want to heavily edit a photo I would always default to Photoshop. It is quite easily to use, in my opinion, and there are loads of tutorials if you do not know how to do something. A free alternative would be something like Gimp (I think it is called that?) It is basically Photoshop minus the branding and some of the fancier features. Bu again, as stated before, it depends on what you deem as editing.