The last couple of days I've playing around with MagicaVoxel. It's a steep learning curve but after few hours it proves to be a real intuitive voxel editor. Projects can be exported in a number of 3D formats but also as PNG. Best of all, it's free.

MagicaVoxel - https://ephtracy.github.io/
Little Dancing Droid made in MagicaVoxel and rigged in Adobe Mixamo