There are two conversations to be had:
Which API you as a normal user should be using in the tablet driver and in your applications
Which API you as a developer should use to create a pen-aware application on windows
By default I recommend you use Windows Ink unless something forces you to use WinTab. And if you use WinTab I suggest you only use it for a specific application.
Remember that in windows you have to configure windows ink in the driver AND in the application. These have to match settings. More here: Windows Ink
Wacom published a page with frequently asked questions about WinTab:
https://developer-support.wacom.com/hc/en-us/articles/12844524637975-Wintab (archive)
Here's a small snippet of the relevant section of the doc
Please read the document for the full details.
But here are a few things that stand out to me:
It is a well understood and stable API
There are wrappers or many languages (C#, Rust, Python) that let you talk to the APIs.
I had a relatively simple time incorporating it into my test drawing app called WinTabPainter.
You can find many projects that use WinTab
It has been difficult for me to find clear examples of how to use the Windows Ink API. Most of the code is heavily focused on the inking features - which is great but not on what I need which is a way to get the pen position, pressure, tilt data, etc.
So at the moment, I intend to continue to use WinTab until I find an easy way to consume the Windows Ink APIs.