Like others have said, being unbiased is difficult, but I'll try. First, Linux v FreeBSD is really tough, so I will instead approach this from Debian v FreeBSD.

I really like how easy Debian on the desktop is: install it, apt-get install xfce, and I have a nice desktop. It's very easy to add Adobe Flash, Steam, Skype, etc.

The FreeBSD desktop isn't as nice. You can add things like Flash and Skype on FreeBSD, but you have to fight harder and often use the Linux emulator. We're missing nouveau, I've had some kernel panics with the nvidia binary drivers (caused by nvidia's own shoddy code, not FreeBSD's fault), there's a lot of missing and unstable features due to developers primarily targeting Linux these days (Thunar's file refresh is glitchy and often fails to update, Thunar volman only really works with udev/Linux, mousepad crashes when you open a file an even multiple of 4KiB due to a bug in their code and a quirk of Linux mmap, livbte-based terminals tend to crash sometimes when you open them due to a bug somewhere between libvte and FreeBSD's /bin/sh, file-roller explodes when you try and extract large archives, Firefox has freezing issues with loading gigantic images unless you set MOZ_DISABLE_IMAGE_OPTIMIZE=1 in your environment, on and on.)

And it's also not really configured well out of the box for the desktop. I have to make this org.freedesktop.consolekit.pkla file and add entries to it in order to get the restart and shutdown buttons in Xfce to work. I have to create a fontconfig/fonts.conf file and substitute Helvetica with Sans in order to get Firefox to anti-alias text on web pages. And so on.

You are also doing all the setup from scratch. You install xorg, you install your video drivers, you set up xorg.conf, you create .xinitrc, you install a display manager if you want one, etc. This is both good and bad. It's great if you love tweaking your system, it's bad if you just want to throw it on a box and run it.

Moving on ... I really, really appreciate Debian's branches. If you install Wheezy, you can get security updates for packages, but not get version bumps. With FreeBSD, you have to choose between "the packages made at release time", or "the absolute bleeding edge." These updates can and do break workflows, especially on the desktop (Firefox pushed Australis on me, ibus moved to this braindead, slow-as-molasses super+space IME changer, etc.) The actual package installs are about the same for binary (apt-get vs pkg), but I much prefer FreeBSD's ports for building software (which is great when you need to patch software bugs.)

But if you're patient and good at fixing problems, you can end up with a rock-solid desktop. And hey, maybe PC-BSD will save you all of the above steps, too. I kind of look at FreeBSD vs PC-BSD as I do Debian vs Ubuntu: I'd rather know how things work than have it all done for me.

In terms of features, I really like FreeBSD's ZFS, even though it does eat a lot of RAM. Snapshots, whole-disk encryption on root, encrypted swap, mirroring/striping/RAID even across different disks, easy resilvering, etc. I also really like pf a whole lot more than iptables, as I find the syntax a whole lot more readable and flexible, although I will lament that FreeBSD's pf ships with ALTQ (QoS) off by default. I prefer the base system being maintained by the FreeBSD team. I like the consistency, the minimalism, and the great documentation.

Whenever I spot a difference between FreeBSD and Linux, I almost always favor the former's design: /dev/random behavior, jails vs cgroups, SO_NOSIGPIPE socket opt instead of needing the MSG_NOSIGNAL flag, etc.

I like that FreeBSD avoids a lot of the 'licensing wars' BS of Linux. I have Firefox instead of Iceweasel, I have cdrtools instead of cdrkit (I continue to this day to have issues with burning on Linux), I have ZFS instead of btrfs, we had sound mixing in an OSS fork instead of ALSA, and just in general I favor the BSD/MIT/ISC licenses to the GPL.

I very much like that FreeBSD is much more conservative about major changes, and open to choice, so we don't get things like systemd, Pulseaudio, etc pushed on us before they are ready for production. I used to love this about Debian as well, but they've really lost their way as of late in pushing systemd on everyone before it was ready. I greatly value stability over whiz-bang bleeding edge features. I like that FreeBSD is run by a democratically elected core team instead of by a benevolent dictator (I don't have to read what crazy thing Linus or Theo said today in the news.) I like that FreeBSD isn't balkanized into hundreds of different distros. I love not having people telling me to say "GNU/FreeBSD" whenever I mention FreeBSD. I like that third-parties like Redhat don't exert so much control over upstream.

I like the community of FreeBSD more, as it feels that most of the members are more technically oriented. Distros like Ubuntu have brought in a lot of users with little to no experience nor interest in learning the unix way of doing things. I'm not saying this is a bad thing, or that I think less of eg Ubuntu users, just that I prefer the company of sysadmins and developers over gamers and web surfers. I dislike that I can't really discuss the OS with anyone in real life, because it's too niche.