Which CAD software you should start with?
I began learning different modeling basics a few years ago. It depends on what you think of 3D geometry, which will determine which modeling software is suitable for you. The "best" software depends on what kind of 3D object you want to create, and of course your taste. Keeping that in mind, here are a few suggestions. I am just suggesting them, you are the one who should decide which one satisfies your requirement and dive into it.
If you are just getting started with 3d modeling and you are just getting familiar with basic concepts try TinkerCAD. It is well proven that TinkerCAD is one of the best options for beginners. There are simple online tutorials and you can start designing basic parts quickly. Although there are limitations to this software but it is a suitable environment to get started. You have the possibility to save as STL file for 3D printing.
If you want to create Artistic 3D models, the following software can be the right choice for you:
Blender is a free and open source software for Windows, Mac, and Linux. This is a powerful program, and difficult to learn. It is easy to fix and make small changes to STL files. This 3d software is used for creating 3D models and video games.
ZBrush is a totally different software. It has a complicated UI, but working on it is like working with clay and wax. It is not easy to learn but it is a very capable software for sculpturing. Working with ZBrush is a lot of fun.
Lightwave, 3DS MAX, and Maya are professional 3D modeling packages typically used for movies and TV. These programs are for 3D modeling professionals. Due to fast rendering engines, they support advanced features such as reflection and refraction, radiosity, caustics, and render nodes. These software packages have been used in blockbuster films such as Avatar and Iron Man.
For creating Engineering 3D models, the following software might be the one for you:
Sketchup was Originally made for architectural projects. it is easy to learn, but it has limitations compared to other 3D software. It is not recommended for creating files in 3D Printing.
OpenSCAD, OpenJSCAD, and ImplicitCAD are all Programmatic CADs. These tools require a programming language background to create objects. This software has some real advantages for 3D printing due to using constructive solid geometry. The best thing about this software is that they are free.
Rhino has become very popular in the 3D modeling world. converting file types very reliable in Rhino. Users with any level of expertise can customize and automate Rhino and extend its capabilities.
There is numerous other worthy software for 3D modeling. You need to dive in and search for yours.