There are lots of 3D CAD options — one list:
and we of course sell:
What sort of work do you wish to do? How do you wish to approach it?
I will note that there are two separate tasks/programs:
- CAD/CAM — arguably a comfy desktop w/ large screen and keyboard and mouse is well-suited for this (one of my first-world problems is finding a CAD/CAM setup suited to my use of a tablet w/ a stylus while seated on the floor at the coffee table in my living room)
- machine communication/control — inexpensive (old) laptops are quite popular for this, and one doesn’t mind so much when a tool or endmill is dropped on something which is already dinged up a bit
And to my mind, the best thing for the latter case is to simply install and set up an inexpensive computer, ideally one which is suited to the rigors of a shop environment, and leave it alone and just use it, until there’s a reason to update.
A desktop, with ports and fans and multiple connections and wires isn’t great for a shop — a tablet, ideally fanless (sealed) is much better.
For a bit more on this dichotomy see: