To be honest, never used Gentoo or LFS. Slackware, on the other hand, is my main OS.
It is customizable to the very end, as every OS you mentioned.
Packages are not always very new, it has a rather conservative version policy, but it's always possible to download and compile from source. By default, it is quite secure and can be hardened, since you have control over everything.
I hope this short insight helps.