As always, the question is how, and what are you going to use it for. Each platform has their merits.
If you want the most mobility, and the pencil experience, the iPad is definitely the way to go. However iPadOS still has more limits than macOS or Windows. For example, if you want to 3D print, most slicers aren’t available on the iPad, and the amount of CPU power and RAM you can have at maximum is more limited. It’s completely fine for simple / medium complexity models, but once you reach multiple thousands of bodies in a project, it will start to show it’s limits.
On mac and Windows you can have higher specs (though, usually at higher price). More storage, more CPU and RAM, more GPU power, but you are sacrificing some / most of the mobility (depending on if you go for a Laptop or a full Desktop build). But more software are available (CNC, Slicers etc), as well as more driver support for other input devices (Spacemouse, Wacom tablets).
In the end, it’s up to you, which platform fits you the best. With Shapr3D Cloud you can access all your designs on every platform, so the key very well could be having multiple devices.