Twitter Bootstrap or Zurb Foundation for RailsApps?
blog.railsapps.org
blog.railsapps.org
This assumes the primary reason you are using a framework is to get the niceness of an infinitely nesting responsive grid and you care about semantic HTML.
Putting the grid in your LESS or SCSS is so much nicer than littering your HTML with "large-4 columns", etc -
I'm currently using Bootstrap in two very different projects. One is an internal admin site where we have managed to get very far just using Bootstrap components in the HTML without any custom CSS at all. It's an AngularJS project and with Angular directives for Bootstrap (http://angular-ui.github.io/bootstrap/) you can use Bootstrap like any native UI toolkit and if you don't need a customized look and feel you can get by with the defaults or just add a Bootstrap theme (http://bootswatch.com/) on top.
Another one is a large application with lots of LESS stylesheets and themed for different clients. By building our custom UI components in the same way as Bootstrap components are built we have managed to keep it very easy to customize for different themes. Bootstrap provides whole lot of variables as customization points and we have added a bunch of our own on top. By changing those variables we can create new themes very easily.
For choosing Bootstrap vs Foundation, just pick one you like. More importantly, use the components provided by the framework as much as you can. When you to roll your own components, make them in the same modular fashion as the framework components. Put components in their own files and namespace them with classes. This way you can keep things nice and modular, and your stylesheets don't turn into an entangled monolithic blob that is difficult to maintain.
As far as foundation vs bootstrap I've used both tend to prefer foundation.
The only benefit bootstrap has over foundation (imo) is the huge number of plugins that already exist. I had to adapt datepicker, xeditable, datatables.js (the worst offender), etc in order to play nice with F4.
Aside from the snazzy 3rd party UI elements (F4 has some in the playground), F4's semantics rock my socks.
F4's docs also explain damn near every line of SASS you'll ever need, so this should fit perfectly with a rails project. All of my work has been in PHP.
Susy should not be compared to Bootstrap/Foundation since it is just a small grid system and not a full blown framework. It can be compared to something like Bourbon Neat.
[1] http://www.kickstarter.com/projects/909377477/learn-ruby-on-...
https://www.google.com/trends/explore?q=twitter+bootstrap#q=...
On that basis, I'd go with Bootstrap.
You don't need to use SimpleForm for every form in an app.
Also, you aren't restricted to using SimpleForm helpers when using simple_form_for. You can use input_field, label, etc. anytime you want to.
Foundation uses SASS, is more modular in approach, is much easier to re-skin, and has a better grid system.
Bootstrap uses LESS, has much more mind share, more plugin and theme support, and has better default styling.
Both are great frameworks. I tend to use Bootstrap for prototyping, and Foundation for production.
Zurb is awesome, but I'm using Semantic UI now. It's new, no V1, but I enjoy working with it more than any other web framework I've used.