I think that Linux has an advantage over FreeBSD, mostly because it has a Stable release, ...
"A" stable release? It has several dozen releases: RedHat, CentOs, Fedora, Suse, Ubuntu, Debian, ...
FreeBSD also has stable releases. Strangely, they are called "-RELEASE", while "-STABLE" is actually a development branch.
Actually, it is virtually impossible to even define what you mean by "Linux". There are so many Linux distributions, with varying quality and goals, with varying distribution models (some are commercial but you get excellent support, some are free, and you get community support, or nothing). So for the sake of this discussion, let's restrict ourselves to the major Linux distributions.
The fact whether a release is called "stable" or not is not an inherent indicator of anything. In particular not of quality. I could write an operating system, call it "stable", and it would still crash all the time; that reflects on my skills, not on the name. I could also call it "elephant", and it wouldn't have a trunk either.
... widely avaible on many mirrors,
That really doesn't matter. If I'm a RedHat customer (and I have been for many years), I can nearly always get to the RedHat site; it is very rarely down. Same with other distributions. Mirrors were a good idea in the early days of the internet, when servers were unreliable, and cross-continental bandwidth or transoceanic bandwidth was sparse. I presume the major distributions use CDNs (content distribution networks, the same technology that Netflix and Youtube use), or their own mirrors, so you can get to the data efficiently and reliably.
But the same works for FreeBSD. I don't remember the FreeBSD download sites ever being down when I needed them.
and the package manager is always up and faultless (really very working around the clock).
Same is true for FreeBSD, as far as I know. I haven't had any problems with "pkg" that 5 minutes of reading the man page didn't solve.
Linux is powering many Servers, and it works.
It powers the vast majority of all servers, with Windows far behind in second place, and all other operating systems irrelevant.
Security is however a lack of Linux, because this is a monster of things altogether.
Nonsense. It is perfectly possible to make Linux reasonably secure. In a previous job I worked with lots of large government labs (the ones that do nuclear simulations or intelligence gathering), and they all run Linux clusters. Companies like Google, Apple and Amazon use Linux for their internal servers, and you haven't heard about data breaches due to Linux bugs there.
Now, for an individual user who has no clue and doesn't know how to administer a computer ... it might be different. But I don't care, since I'm not that user. If Linux is a bad solution for him, maybe he should use something else (like MacOS or OpenBSD).
I am surprised that the FreeBSD has very often package services, that are are down, non working, and many things may be changing radically. You'd better not to update too often completely the Server. Base System of FreeBSD is not as stable, but actually may be unstable time to time.
That has not been my experience.
What do you mean by "stable" here? Absence of crashes? Once I stopped using my FreeBSD server as a wireless AP, it has not crashed a single time (but my longest uptime has been about 6 months, due to power outages longer than the UPS can handle). But a well-managed Linux machine can also run for months without crashing.
Or do you mean stable against major upgrades that disrupt applications? That's a very complex question. Linux distributions have different upgrade philosophies; FreeBSD has an yet a different one. Layered software you put on top of the OS distribution are even more diverse. There is no simple yes-no answer.
However, more People means more People to fix bugs and keep running.
That is a very hotly debated questions. Does open source, and the fact that many eyes can see the code actually mean that it is of better quality, and has fewer bugs? The vast majority of people do not look at the code; and many parts of the code (in particular the most difficult ones) are very complex and are understood only by a very small number of people. It may actually be a better idea to have a small number of well-selected, well-trained, motivated and competent people to write and maintain code.
The same argument can be made for and against blobs. Rufwoof seems to make the argument above that blobs are inherently insecure. That is nonsense when taken in the pure form. They are exactly as secure or insecure as you trust the author of the blob. And it is not at all clear whether I can trust the author of a blob (be it LSI or Nvidia) more or less than the author of unreadable and complex code (be it a RedHat or IBM employee who contributes to Linux, or a volunteer who contributes to *BSD).
Well, FreeBSD ok, but LINUX ok too.
Conclusion - "Comparing": likely FreeBSD more secured. LINUX is too highly stable.
Complete and utter nonsense. FreeBSD may be OK, and it may not be OK. The same goes for Linux. You simply can't "compare" them, other then in details. Even saying that one is more secure and the other more stable is nonsense; it depends on intended usage.
The real question is: does the OS fulfill the expectations of its users? Those expectations can be sorted into various categories, such as reliability (absence of crashing, uptime), availability (includes reliability, but also includes downtime for upgrades and maintenance), security (not easy to hack, exploits are quickly fixed, designed to be safe), data reliability(the file systems and device drivers such as RAID are built well, can handle device shenanigans, and don't grenade your file systems), cost (include the cost of support if it is needed), and most importantly features (which is in particular availability of particular software). Those expectations have to be seen in light of the needs of the user; the single biggest distinction there is desktop/laptop versus server/cluster/cloud, but there are many more fine-grained distinctions.
I am getting VERY tired of the same small number of members of the forum always starting these pointless debates with nonsensical blanket accusations and dumb generalizations. Dear Spartrekus: Please just shut up. You are not doing anyone a service by posting inflammatory nonsense, even if you are perhaps trying to learn by reading the answers.