Looks like we reached (and even exceeded) 100 votes. Just a couple comments.
With 62% for git, we are nowhere near the 80% to 95% figures we often see for pure software development. I'm not all that surprised, this was also the point of this thread: having a look at what EEs use for version control (when they use anything.) One of the reasons is probably that a number of them work at companies in which other systems are in use, which is more common in other fields than pure software dev.
Still regarding git, as others have noted here, a significant fraction of users are probably using this more as a remote "incremental" back-up tool (many using github due to its popularity) rather than as a true version control system.
For CVS, there is no contest here, except for a few organizations that still use it, it has been largely superseeded by SVN (for a similar centralized approach) for a long time now.
We can note that SVN is still used for a non-negligible fraction of people, something that seems consistent with what I've seen in industrial settings. The fact that it's a centralized system, with its pitfalls, is actually still seen as a benefit for some organizations, or even a non-negotiable feature.
The "other" choice probably includes in-house solutions as well as commercial ones, and it's not a negligible fraction either.
I'm not sure why Mercurial has so few users. It was actually released slightly before git initially, and clearly git was not meant to "compete" against it as (AFAIK) Linus Torvalds didn't even really know about it at the time he was designing git, and he never cared. The fact Mercurial was written in Python is likely a factor that would have made him ignore it completely anyway.
Whereas I don't like Python much for a number of reasons, I do like Mercurial. It's clean, it's simple, it's consistent, and it doesn't have myriads of options to shoot yourself in the foot like git does. I haven't really ever seen clear points/facts against it from people not using it. They are just not using it, but for no real reason other than popularity of other tools. I found the following article:
https://bitbucket.org/blog/sunsetting-mercurial-support-in-bitbucket (which was linked by some poster here) pretty idiotic. The introduction itself shows a complete lack of knowledge of Mercurial, yet the article is supposed to explain why abandon it. Quoting:
The version control software market has evolved a lot since Bitbucket began in 2008. When we launched, centralized version control was the norm and we only supported Mercurial repos.
Mercurial is absolutely NOT a centralized version control system. It's distributed just like git is. Face palming introduction. The only real rationale for abandoning it was just lack of users, nothing technical. Whereas it has little popularity compared to git, it's still used by a number of very large organizations, including Mozilla.
Back to git: I personally think this was designed (and is adapted to) much more for maintainers than for contributors, which absolutely makes sense knowing why and what for Linus designed it.
Finally, regarding the numbers themselves, we can see that version control doesn't seem to interest/is probably still not used by many EEs. This is not very surprising either. Generally speaking, a strict process for handling hardware modifications is still a relatively rare thing in many companies (except those in regulated fields such as avionics, medical devices, etc.) from what I've seen. Whereas it can absolutely be done with other tools than version control systems, I've found that it was pretty often not done at all, or at least with too little discipline.