Both of these starter themes come from people at Automattic (the WordPress parent organization), so they both provide a solid foundation for theme build-outs. The major difference between them is that Toolbox assumes you’re going to build a child theme on top of it. Underscores, however, is right up front about saying, “Don’t build a child theme on this.”
Even Starter Themes Have Some Bloat
By far, the most surprising thing about both these starters is how much they give you to start with. They both come with quite a few functions already defined, and a surprising amount of CSS. You’d never suspect it, given the spartan look of them out of the box.
It’s an eye-opener to see what the Automattic theme folks consider essential to include. Theme support for post types and backgrounds, head links and body classes for various feed types, CSS for screen readers, right-to-left language support. It’s all there.
WordPress Has Even More Bloat
As I was working on these, though, what began to bother me was the amount of extra stuff WordPress itself inserts into each page. Stuff that might or might not be useful, depending on what the site is about. Once you start adding plug-ins, things really start to expand rapidly. It’s like the big bang happening in your browser.
I started finding myself slightly obsessed with figuring out where all this stuff was coming from and seeing if I could get rid of it. If you firebug this page, you’ll see a huge load of crap in the section of the HTML. Take a look at all this: