Not so many times ago I changed RedHat for slackware. And now I'm happy
So, look here:
1) Slackware has simpler package system. It's without checking of dependences.
2) RedHat has some problems with localization. It has many files and folders which are should be changed when you want to use some language which is not English. (I'm from Russia). When you use slackware there are only 3 files which are needed to change.
3) When you want to change your kernel in RedHat you'd better to use special kernel from redhat.com. For slackware you can use original kernel from kernel.org.
4) Slackware has BSD like initialization. I think it more usable then SysV initialization.
5) Slackware has not GUI config tools. But I don't need these.