When comparing Mithril vs Vue.js, the Slant community recommends Vue.js for most people. In the question“What are the best client-side JavaScript MV* frameworks?” Vue.js is ranked 1st while Mithril is ranked 6th. The most important reason people chose Vue.js is:
Vue can easily be integrated with other front-end libraries. This makes it an extremely versatile tool and it's easy to fix its shortcomings or missing features by just plugging in another library.
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 Can be used with any front-end stack
Vue can easily be integrated with other front-end libraries. This makes it an extremely versatile tool and it's easy to fix its shortcomings or missing features by just plugging in another library.
Pro Single file component
Very useful.
Pro Lightweight
Vue.js weighs in at 16kb min+gzip.
Pro Vuex store, events system
Pro Reactivity system
Pro CLI and Webpack integration
Pro Responsive server-side rendering
Since most of the mainstream server-side rendering implementations are synchronous, they can block the server's event loop when the application is complex.
Vue implements streaming server-side rendering, which allows you to render your component, get a readable stream and directly pipe that to the HTTP response. This allows you to have a responsive server and decreases the time your users have to wait before they get your rendered content.
Pro Supports inline templating
Although you can build components in JavaScript files, you can also use inline handlebars-like templating in your HTML views where simplicity is often a more sane choice.
Pro Can be made even lighter
Since the template-to-virtual-DOM and compiler can be separated, you can compile the templates in your machine and then deploying only the interpreter which is 12KB minified and gzipped.
Pro Support for both templates and JSX
You can choose to use either a templating language, or if you feel it's necessary to drop on a lower virtual-dom level, you can use JSX. This is simply done by replacing the template
option with a render
function.
Or alternatively, you can embed functions inside templates by using the <render>
tag.
Pro SEO friendly
Starting with Vue 2.0, Vue supports server-side rendering. This helps with SEO a lot, since the views are rendered directly on the server, which are indexed by search engines.
Pro VueRouter
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 Poor typescript support
Very basic typescript support.
Con Very enterpris-ey in design and tooling
