I used to use Slackware.... before there was a RedHat that is. I also use Debian on some servers (mostly on old Sun Sparc hardware) which is an excellent distro. Without Debian there wouldn't be a Knoppix, which is probably the best CD distro.
I prefer RedHat on servers and desktops though. It is more widely used and has more support across the board (applications are usually ported to RedHat first). There are too many other reasons to list as to why I prefer RedHat.
I started using Linux before there were any distros. SLS was the first distro I used. Then when Slackware came out it was a far better distro than SLS. Then RedHat came out and I found it to be better than the first Slackware version. I switched back and forth up until RedHat 3 and they've been out front of everyone from that point on as far as I'm concerned. And without RedHat there would be no Mandrake that so many people like (I'm not a Mandrake fan by any stretch).
But I think it's great that people try different things. I just hope in their trials they give RedHat a look. Those RedHat guys should pay me for marketing!