When comparing Bootstrap vs Materialize, the Slant community recommends Bootstrap for most people. In the question“What is the best CSS framework?” Bootstrap is ranked 2nd while Materialize is ranked 13th. The most important reason people chose Bootstrap is:
The grid layout with the predefined CSS elements and JavaScript components make it easier to have consistency across different browser versions and even different devices.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Consistency across browsers
The grid layout with the predefined CSS elements and JavaScript components make it easier to have consistency across different browser versions and even different devices.
Pro Responsive design philosophy
Bootstrap is developed to be instantly compatible with all sizes of screens, so you don't have to worry about which device the user is accessing your site from. Yet if you prefer, you can disable responsiveness of Bootstrap.
Pro Well documented
Documentation is thorough, well organized and full of live examples and templates ready for use. Every component and every part of the framework is explained and covered in depth.

Pro Custom builds
If you don't want to download the full Bootstrap framework. Custom builds of Bootstrap can be created, including only the desired CSS, CSS components, and JavaScript components. This can be done directly from the Bootstrap website by simply choosing what components to download.
Pro Designed to get a site running quickly
Bootstrap is designed to get a site up and running quickly. Each of it's components is pre-configured to help with getting a site up and running quickly.
Pro Great community
Bootstrap is very popular and has a large community. As a result of this it is much easier to find help with anything you might need. This also gives you a treasure trove of prebuilt components to use and add to your site.
Pro Supports responsive embeds
Allows easily adding responsiveness to <iframe>
, <embed>
, and <object>
elements.
Pro Easily make professional looking websites
Bootstrap makes it easy to learn how to make professional looking websites. It can even make code junkies semi-enjoy design.
Pro Customizable
Bootstrap can be customized in a variety of ways. Either by overriding the default CSS styles with new CSS styles or by editing the .scss
Bootstrap files.
Pro A wide variety of themes available
To help you avoid the "Bootstrap look", there are many resources that provide a great selection of themes and templates for Bootstrap.
Pro One of the most popular ones
Ranked on GitHub as the most starred CSS repository.

Pro Great-looking demo
Pro Device agnostic
Since Materialize follows Google's guidelines for Material design, which in theory is device agnostic, Materialize itself is device agnostic too. It's designed to look good on every device.

Pro Large selection of components
CSS components: Badges, buttons, cards, collections, footer, forms, icons, navbar, pagination, preloader.
JavaScript components: Collapsible, Dialogs, Dropdown, Media, Modals, Parallax, Pushpin, ScrollFire, Scrollspy, SideNav, Tabs, Transitions, Waves.
Mobile-specific: slide-out drawer menu, toasts.

Pro Responsive

Pro Mobile navigation

Pro Nice showcase of sites built with Materialize
Pro Customizable
While the default style is not bad at all, Materialize also gives developers the ability to customize it and fit their own style, while still keeping in line with the Material Design philosophy.
Along with the CSS files, designers can also download the SASS files which can be edited and compiled.

Pro 12-Column Grid System

Pro Included icon font

Pro Meteor.js integration by developers
Pro Opinionated
Material design is very opinionated on how design elements should behave and look. The basics of which revolve around certain visual elements (physics, space, momentum and light) which are used to create specific UX elements.
This is very helpful because it creates a consistent feel without making every design look the same. This can be seen in Materialize too, where each element may be customized but still it keeps the consistent look of the material design.
Cons
Con Large file size out of the box
Bootstrap has an out-of-the box filesize of ~276K, which is pretty large considering it's just CSS. Most of those styles aren't even used in 90% of web pages built with Bootstrap. By only including the required styles it can be trimmed by 70%-75%.
Con Too many classes
Bootstrap's over-reliance on HTML classes for styling can get very messy very quickly. There's also an overabundance of DOM elements which have a lot of classes and are more often than not nested inside DOM elements with even more classes. This gets problematic down the line because the maintainability of the project gets harder when the project starts to get large.
Con Websites can start to look the same
If the initial Bootstrap colors and styles are not changed or edited, different websites start looking the same even if they have nothing to do with each other and they are made by different developers.
Con Hard to customise
It's quite hard to customise Bootstrap using pre-processors like SASS and LESS, the only real flexibility is with typography and colours.
Con Large font sizes

Con Refuses to use the flexbox model
Even though Materialize states that it only supports IE10+, which supports flexbox quite well, with prefixes, Materialize has refused to use Flexbox.
Con Not maintained anymore

Con Large / heavy
267 kilobytes, minified, for the CSS and JS.
Con Deprecated
No longer supported by their maintainers.
