Arch, by far. The only feature I miss is Use flag / ports-like functionality. The entire distro is focused on simplicity (NOT ease of use!), vanilla-ness, minimalism, and tweakability. ABS is similar to ports except, sadly, no config flags. To the person that said ABS was hard, it only takes two commands? One to build the package from the PKGBUILD (another feature, Arch packages are built simply through a bash script called a PKGBUILD, which is very easy to write), and one to add through pacman. Pacbuilder makes this even easier. There's also the AUR for user-made packages.
Right now, the only two things I can see FreeBSD has over Arch are stability and the ports configs. I've never had stability problems under Arch, I can just see from a technical perspective why FreeBSD would be more stable. The rolling release is actually more stable, for me, than most scheduled-release distros. *BSD does a very good job of having rock-solid stable releases, as does Slackware (never tried Debian), but I've had too much misery where I'll upgrade the system and three things are broken, with no clue what caused them... with rolling, I can tell what upgrade broke what, and I can downgrade or at least have a starting point towards fixing the problem. Note, this has never happened with Arch so far
If there was no Arch, I'd likely use Slackware (not as cutting edge, less dependency management means less minimalism since it's more likely that unused packages will be left on the machine, 64-bit version not supported much) or Gentoo (needs more KISS and focus).