Choosing a framework to build a native app on Windows with .NET

By "Native," I mean not using web technologies, either as a remotely hosted website or bundled into a package that is installed and runs locally.

Let's get this out of the way first. 

There is no "best". 

There is only best for your current circumstances and requirements at the current time.

That said, how do you decide what might be best for your circumstance?

Each option has slightly different capabilities. It's essential that you know what capabilities you'll need before you start building. If you don't know what you need to build, it's impossible to say which is best for you. This may make the decision for you. 
Doing the work in advance to fully understand the requirements can save a lot of frustration and wasted time and effort if you discover you need something the framework can't do. 

So, second disclaimer out of the way, how do you decide which .NET framework to evaluate first? 

If the first thing you evaluate does all you need, it's probably fine to go with that. If not, try another.

Q1. Do you think you might ever need to run on more than just Windows?

If Yes - go to Q2.

If No, go to Q4.

Q2. Do you want the software to also run on the web?

If Yes - Evaluate UNO Platform first.

If No - go to Q3.

Q3. Are you primarily interested in building an app that runs on desktop, or on mobile devices?

If Desktop - Evaluate Avalonia first.

If Mobile - Evaluate .NET MAUI first.

Q4. Do you already have any existing apps built with WinForms, WPF, UWP, or WinUI?

If Yes - continue using that. (Unless it's UWP, then go to Q7.)

If No - go to Q5. 

Q5. Are you building a "traditional line-of-business" app or something that could be described as "forms over data"?

If Yes - go to Q6.

If No - go to Q7.

Q6. Are you happy to use/learn XAML?

If Yes - evaluate WPF first.

In No - evaluate WinForms first.

Q7. Do you need to support XBox devices, game pad controls, or ink-based input?

If Yes - evaluate UWP first.

If No - evaluate WinUI first.

Happy evaluating!

Yes:

• The above is probably an oversimplification.
• There may be many situations where you don't go with the first suggested option above.
• It doesn't consider personal preference. But if you already have a preference, you should probably use that. (Assuming it can do all you need).
• I haven't considered support for different programming languages. (But you're almost certainly using C#).

This isn't intended to be a definitive guide. Without knowing your exact requirements, existing skills, and preferences, I can't say for sure. 

I just wanted to share some simple questions that others have found helpful when overwhelmed by the options available.