Before the advent of GraphQL and the Mobile Client, the best Tablets to use were Windows Tablets. SambaPOS only runs on Windows, and trying to use RDP for other platforms is not ideal by any stretch.
Now that GQL exists (SambaPOS V5 only), the answer is not that clear. I still prefer Windows Tablets because you get more value for your money IMO (ie. ~$200 for a full computer (10" Tablet with Keyboard) running Windows 10 cannot be matched by any Android or iOS device for capability, flexibility, and price).
With GQL, you can run Apps on any platform for which an App exists. That said, it depends on what Apps have been developed, whether they are available for the platform, and whether or not they meet your needs.
For example, if the SambaPOS Mobile Client App (currently Android only) does what you need (currently limited to Table-side Ordering), then you can get away with using devices that cost less than $100, or even have your Staff use their own Device (if they let you install the App).
Another example is QMX which runs on ANY platform that has a Browser. It contains several “Modules” including POS, Kitchen Display, Customer Display, Reports, Timeclock, etc. QMX runs on my 5" Android Phone (Galaxy J1 Mini) or my iPad just as well as any Windows Tablet.