I’ve been using an iOS app called iDraw (now called Graphic when Autodesk acquired it). I use it for creating 2D vector graphics for apps and web site I create. It’s great since Graphic (iDraw) is available both on iOS and MacOS.
Recently, I’ve been trying to learn how to create 3D graphics on MacOS for some personal home projects using SketchUp. For personal projects, SketchUp is actually free. I started looking for an affordable 3D graphics app that runs on iOS (especially on the iPad).