Debian is very good for servers and routers... Very good securtiy
Redhat is for servers, for coding and good as workstation.
The best Linux distribution and bestseller
Slackware is for more performance, u have to know technical stuff, like compiling the kernel, partitions.... to install it.
It the best Linux distribution, I ever saw.
The performance is 15-20% better, cause this distribution downloads the source and compiles it for ur computer.