I also like both FreeBSD and Debian (have no real experience with the others). But on performance it varies a lot by workload. To take two examples: over the years at any given point in time, FreeBSD has had a better networking stack than Linux, but worse scalability to large numbers of cores. Though there is some ongoing sponsored work on the latter [1,2].

[1] http://www.ixsystems.com/whats-new/freebsd-foundation-and-ix...

[2] https://news.ycombinator.com/item?id=8123512