UModeler is the best 3D modeling and prototyping solution in Unity.
UModeler is an extension to Unity that allows you to easily and quickly create models and prototypes. With UModeler, you can create static mesh resources and prototype game levels without the need for any other external DCC tools. In addition, UModeler supports not only gadget modeling, but also sketch-based modeling, allowing you to draw a 2D shape on a flat surface and then shape it into a 3D shape using an intuitive approach. Any polygons are automatically triangulated and fed into the rendering pipeline even if they contain holes inside. This will save you a lot of time. UModeler includes about 90 tools for modeling which will allow you to easily create, transform and edit models in Unity.