What's Your opinion? Which distro is the strongest competitor to slackware? Not in financial power nor market share, but more in flexibility, modularity, freedom to customize, documentation and such benefits.

Maybe you're using your choice beneath slackware on a 2nd comp...?

Only Gentoo or Debian really come close. Maybe Rock Linux, though that's a bit closer to LFS than a binary distro.

Arch linux is as flexible as slackware, but most flexible and customizable is Linux from scratch http://www.linuxfromscratch.org/ ;-)

I have heard gentoo is the bees knees from its fanbois but never been able to get it to run. The fact of the matter is compiling (correctly) = stable.

Plus lets face it, slackbuilds turn chicks on. (mine anyway)

i use debian at work for the server. it'd be my second choice of distro. it tends to Keep It Simple, so i like it in the same way i like slackware.

there are only a few differences i see on a daily basis.

1. deb has different locations for the rc.* files.
2. it didn't come with a large base system (i installed it using the ftp install). this means i have to install a lot of software, plus its dependencies, with apt-get.
3. deb seems to have a larger official software base. in slackware i go to slackbuilds (via sbopkg) for all the non-slackware-official software i use in debian.

i understand it has othere differences. like debain patches it software quite a lot. but that's never affected me. (i never went through the openssl patch and panic nightmare with debian).

I don't think there is one.
For example, Arch is certainly missing the documentation part.
Debian is missing everything else.
I would say that CRUX is the closest one to Slackware, but it's not really that close.