… Helvetica Neue followed by the 10.11 version of San Francisco. …
Thanks.
It appears that the face in 10.11 is more lightweight than the face in Yosemite. (Viewing the screenshots, not the OS, on a 17" MacBookPro5,2.)
… I wouldn't be surprised if Apple is still assessing the look and feel of iOS and OS X.
Recalling comments from a few months and a few weeks ago, I'm inclined to view the entire Yosemite phase, including all 10.10.x releases to come, as one long beta.
I'll probably extend that thought to treat releases of 10.11 as part of a longer multi-version beta, which began with 10.10.