Both let you write interfaces in C# and XAML for several platforms, but with different philosophies. The right choice depends on where the application must run and how it should look.

Key differences

• Rendering: MAUI uses each system's native controls; Avalonia draws everything itself, with an identical look everywhere.
• Linux: Avalonia supports it officially; MAUI does not.
• Mobile: MAUI was born for phones and tablets, with deep integration into native APIs; Avalonia supports iOS and Android, but its strength is the desktop.
• Web: Avalonia can run in the browser with WebAssembly; with MAUI you go through Blazor Hybrid.
• Support: MAUI is part of .NET and maintained by Microsoft; Avalonia is open source with a dedicated company and commercial support options.

XAML side by side

<!-- .NET MAUI -->
<VerticalStackLayout Spacing="8">
    <Label Text="{Binding Name}" />
    <Button Text="Save" Command="{Binding SaveCommand}" />
</VerticalStackLayout>

<!-- Avalonia -->
<StackPanel Spacing="8">
    <TextBlock Text="{Binding Name}" />
    <Button Content="Save" Command="{Binding SaveCommand}" />
</StackPanel>

The concepts are the same, the control names are not: anyone who knows one learns the other quickly, and ViewModels written with CommunityToolkit.Mvvm can be reused unchanged.

How to decide

• Consumer smartphone app with a native look: .NET MAUI.
• Desktop business app that must also run on Linux or Mac: Avalonia.
• Operator panel on an embedded Linux device: Avalonia.
• Migration from WPF to more systems: Avalonia, closer in concepts.
• Team with strong web skills: MAUI Blazor Hybrid.

There is no best framework in absolute terms: there is the one that suits your users and your devices. A small prototype with both, on the most complex screens, clears up doubts better than any table.