When comparing Mithril vs Webix, the Slant community recommends Mithril for most people. In the question“What are the best client-side JavaScript MV* frameworks?” Mithril is ranked 6th while Webix is ranked 14th. The most important reason people chose Mithril is:
Most other frameworks either offer a huge API to deal with model and view synchronization, or defer to other libraries & plugins to cater for relatively simple use cases. Mithril's API is tiny but complete. The natural reaction is to assume something is missing, but as you build you realise you incredibly fast, powerful and rich applications can be built using nothing but Mithril.
Specs
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Pros

Pro Small, easy to learn API
Most other frameworks either offer a huge API to deal with model and view synchronization, or defer to other libraries & plugins to cater for relatively simple use cases. Mithril's API is tiny but complete. The natural reaction is to assume something is missing, but as you build you realise you incredibly fast, powerful and rich applications can be built using nothing but Mithril.

Pro Fast rendering
Mithril's loading times are very fast. This is because it's templates are compiled first and then served to the browser and because it uses a virtual DOM. The virtual DOM is a virtual tree containing all the nodes of the real DOM, every time anything changes in the virtual DOM, Mithril does not re-render the entire (real) DOM, instead it just searches and applies the differences.

Pro No need to learn another syntax to write views
Most MVC frameworks use HTML templates to render their views. They are good and useful because they are easy to read and understand. But they add more complication to an app because it's practically a new language and syntax that needs to be learned.
Mithril argues that separating markup from logic is just a separation of technologies and not concerns, so you can write Mithril views in JavaScript. Writing them in JavaScript also makes it easier to debug them (HTML templates can't be debugged).

Pro Familiar to people used to MVC
Doesn't lock you into any complicated conventions or structures, only one function is required to create either a Controller or a View. You're free to implement your architecture exactly as you want, so you can focus on the purpose of MVC, making connections between computer data and stuff in the end user's head.

Pro Small size
Weights just 8Kb gzipped and has no dependencies. A reactive stream module can be added for one extra Kb.
Pro Great documentation
Mithril has a large and expansive documentation despite it's relatively small API. Mithril's GitHub repo has more documentation than actual source code. None of that documentation is auto-generated
Pro Allows a smooth transition from other UI frameworks
One thing you need to start using Mithril is just a DOM node. With Mithril a developer is able to introduce the library step by step.
Pro Allows you to choose which JavaScript libraries to integrate in your project
Mithril gives to the developer the flexibility to chose the best JavaScript library to use for a specific task.
A huge framework like Angular instead forces you to use their API, which does not necessarily evolve as fast as the JavaScript ecosystem. Therefore you may end up in case when you are stuck using an API which is just not the best in terms of performance
Pro Can be used without build systems
It's plain old JavaScript, can be used without webpack, gulp or grunt, just include it into your HTML and start writing your app.
Pro Does not force you into a predefined structure
Mithril's API is pretty small compared to other frameworks. It forces developers to solve problems in JavaScript rather than in Mithril. Other frameworks with massive APIs force you to think in a way that suits the framework. Mithril doesn't do that.
Pro A lot of widgets
Webix is one of the most extensive UI component libraries, second only to Sencha ExtJS. Not only considering the number of widgets, but also the API methods for manipulating these widgets.
Pro Views can be constructed using JavaScript without HTML
The most common way of working with webix is to create a JSON configuration of your view in JavaScript. When you use TypeScript, you get complete typechecking and intellisense in your IDE.
Pro Seems to be quite stable
Even the most complicated GUIs are bug-free most of the time.
Pro Webix Jet
The webix Jet library adds all the required features for SPA development (routing, template loading, ...)
Pro Extremely simple to implement.
To get started is extremely simple. It has a low learning curve.
Pro Mature project
Regular updates and releases.
Pro Great support from the webix team
The company behind webix is really quick in answering any questions you have on their forum or via email.
Pro Awesome responsive material skins
Great design and icons pack.
Cons
Con Small API can make it unsuitable for larger more complex projects
Mithril's small API and small number of functions while helpful for small projects and applications where speed is needed, can add another layer of complexity in larger more complex applications where a more extensive API is needed out of the box.
Con Commercial license
It's not free for commercial applications.
Con Not very popular
Not really a reason to not recommend it. But it has still a small user base. It deserves a lot more attention.
Con Not modular
The library is not modular (except for some additional more complex widgets). If you only need a few widgets, you still need to include the entire library.
