This framework is best for developers who really want to start building solid foundation for themes. Genesis is actually premium/paid framework, but it worth the money spending on. The architecture of Genesis is very extendable and give developers control over every aspect of the design.
Everything loading scripts, building theme blocks, sidebars and custom post types can be easily modified, added or deleted using hooks. This framework is not like standard WordPress development of theme in which you follow procedures like modifying header,footer and page/post template files. Here, in Genesis, you will be working on child themes only.
Core framework, will be installed inside themes folder as a parent theme. When you download framework from Studiopress, you will be able to download sample child theme as well. All you have to do as a developer, is need to modify this child theme for your requirements. for most part of your theme, probably you will be working on adding/removing hooks in your child theme’s function.php file only. Fortunately, Studiopress provide nice documentation about hooks and filters you can use to achieve what you want. There are other sites, such as, one of my favorite http://genesissnippets.com/ provide wide range of examples for most common problems during your first Genesis theme development.
Yes, you may find little bit difficult to go ahead during your first theme development, but believe me once you do that, you will start loving this framework like me.
Checkout Genesis framework here: Genesis framework
Bones framework is open source and available free. Its full HTML5 framework with support of css3 and particularly Saas. By default, It provides mobile friendly and responsive theme. It follows standard wordpress theme development procedures. You will be modifying files rather than using hooks and filters in Genesis. There is no or very little learning curve to start developing your theme with this framework.
There are nice tutorials available to start theme development with this framework. Such as, for starters, this tutorial in http://code.tutsplus.com/tutorials/making-a-theme-with-bones-getting-started–wp-26545 will be a nice start. It comes with preloaded custom post type file to work with any additional post type you may be adding in your theme.
Check out more information about bones here. http://themble.com/bones/
Its a very basic starter theme. There is no learning curve to head start with underescore. Its very simple to work with. This starter theme do not include any css for design. If you install this starter theme, you have to start from scratch to design your website, which may be the ideal way to work in many occasions.
This theme follows WordPress standard theme development procedure, you do not need to learn anything special. It is recommend to add option-tree plugin for some serious level of theme development. Advantage of using underscore is that once you built the core theme one time which you can use for other projects in the future.
Checkout underscore theme page here. http://underscores.me/
Let me know, if other framework you work on and you have good experience with it.