As requested by @rvr, here's a control sample from Lion, the reimagined Lion by @realmacdan, Sequoia, and Tahoe beta 2.

To be more fair to Tahoe, here's a version where I re-aligned the controls to accommodate the new metrics. I've also included Yosemite in this one. (I'd add more, but there's apparently a four-picture limit.)

A few more older ones, plus Tahoe beta 2 dark mode.

Here are some great “reimagined” Retina-resolution images of some older versions of Mac OS X created by @kylehalevi

@siracusa If you had to choose one of these styles to go back to (with Retina-quality, of course), what would you choose? I think Lion might actually be my favorite in some ways.