QEPrize3DDesignStudio has an intuitive, easy to learn interface, and allows you to build fairly complex structures out of different shapes.
When you tap to add shapes together, it feels a lot like building things in Minecraft (especially if you use the cubes), which is good. Anyone with prior experience with that game will probably find QEPrize3DDesignStudio easy to pick up and use.
You can also offset the position and rotation of shapes, so they no longer snap directly, which adds a lot of versatility for modeling. (You could build a ring out of cubes or diamonds, if you wanted.)
I like how you can toggle between solid and wire meshes for each shape, which can totally transform the appearance of your models. (For example, if you made a row of solid cubes, you could change them to wire mesh to make them look like a support strut for a building, or something.)
QEPrize3DDesignStudio also allows you to email (export) your models as .obj files, which can be read by most 3D modeling / animation software for computer, like Blender, Maya, 3DS Max, etc.
One thing I think is really awesome especially, is that QEPrize3DDesignStudio is 100% free! (At the time of writing.)
Really happy they made QEPrize3DDesignStudio. I have been looking for something like this, for about 2-3 years now. There are other shape-based 3D modeling apps like 3DC.io, (which is good also.) but QEPrize3D is an instant favorite, for me.
Many thanks to the devs for their great work!