Just Win32, it is the only one that wont be abandoned in a couple of years when someone at Microsoft decides to make a new UI stack that will solve all the problems all of their previous stacks had.
Here is a good test to see if some new UI functionality from Microsoft will catch on: can you use it with CreateWindow and/or pure C without feeling like someone is hammering nails under your fingernails (so that it can also be bound to all the languages out there that have C interop and/or existing toolkits can build on top of the new functionality without rewriting everything from scratch)? If so, then it'll be UI functionality that you can rely on for the future.
If not, just ignore and stick with Win32. Microsoft will do the same anyway.
Here is a good test to see if some new UI functionality from Microsoft will catch on: can you use it with CreateWindow and/or pure C without feeling like someone is hammering nails under your fingernails (so that it can also be bound to all the languages out there that have C interop and/or existing toolkits can build on top of the new functionality without rewriting everything from scratch)? If so, then it'll be UI functionality that you can rely on for the future.
If not, just ignore and stick with Win32. Microsoft will do the same anyway.