I have a very soft spot for Solaris - first it was the first Unix I really used professionally, and the CDE was a lovely thing to use compared to some of the things I had learned on. I have a sparc 20 with solaris 7 in my basement, for nostalgia's sake.
The newest version has some beautiful features especially for clustering / replicating etc. If you have the money Solaris certainly is a great product.
It is probably because I have used unices first that I like slackware and BSD - slackware is a very unix-like distribution.
BSD is superbly stable, and I removed a lot of hassles in one of my previous lives by moving a whole farm of servers from redhat to BSD - uptime increased dramatically and a lot of mysterious crashes and failures simply never happened again.
I wish I had the time to make them do the same thing where I am now, but I am no longer the person doing the work and I dont think we have a sysadmin skilled enough to succeed
In the end when it comes to my desktop I am just too used to all the windows software I found over the years to want to try to switch to any other I just havent found anything to even tempt me in any category. The mac is another matter.