Depends on how you measure "best". If you measure it by democratic means, namely market acceptance
For servers, Linux is unbeatable. On supercomputers (the Top500 list for example), it has 100% market share.
That should never be a mark of "best".
Even looking at Netflix: The bulk of Netflix runs on AWS, and the a lot of uses Linux.
On the business end, not serving their bread and butter video content delivery where FreeBSD rules.