What is the hardest medium to paint with?

This is for an artwork, and i would like to know which is the hardest medium to paint with, acrylic, watercolor, oils, Ect. So what is the hardest medium to paint with?What is the hardest medium to paint with?
In many ways, watercolors are the mot difficult to paint with. If you accidentally put on the wrong color, you cannot change it as easily. With oils and acrylics, you can just put on another few layers. Watercolor, however, has a beauty of translucency that appeals to many of us. It is also a medium that you can easily take with you on a hike.What is the hardest medium to paint with?
Watercolor...because you work in transparent layers. With most other painting types you can ';rework'; the paint after it is dry by painting over it...you cant paint over watercolor in that same way. Also..with watercolor the ';pure white'; that you use is the color of the paper usually so it needs to be kept blank which can be tricky.
Encaustic painting is difficult because you have to have to keep the wax at a certain temperature. Blending of colors has to be done in little pots over an iron. However, it does allow you to carve the paint later for special effects.
Watercolor or inks because you have to wait for it to dry every time you add colors. If you don't it bleeds. It's also much harder to cover up mistakes. In some cases, it's much easier to just start over. The end result is beautiful, though.
I would think watercolor because it bleeds so easily and it's hard to get a contrast/mix colors.
feces. It smells and you can't get much variety. Much harder than watercolor.
it is incredibly difficult to paint with only water.