I worded that carefully for several reasons. First, because I do deeply respect Kev and you other long-time Scalix wizards. You've all helped me out with my setup. I basically had to take over all of our servers after my predecessor moved on to a new job. I hit the ground running and places like this forum have been a big help.
But another reason that I was careful in what I said was because I didn't want to ignite a flame war over distros.
All I can relate is our experience. I don't know how close Suse Enterprise is to the codebase for Opensuse. I especially don't know how close Fedora is to RHEL. I do know that we had issues with Fedora (major ones). We have had none with Opensuse. For the record, my predecessor moved our mail system from RHEL to Opensuse because he considered it an ideal choice, especially on the "bang-for-buck" metric. Our company Web servers have run on Opensuse for years with no issues well -- another case of deliberately moving from RHEL to Opensuse after careful consideration.
(I'm no slacker, and I'm certainly not a noob, but my predecessor, a rambunctious thundergeek named Ed, was a true gunslingin' propeller head who started out with Slackware back in the early days, so I value his opinion, too. Deeply.)
I went with CentOS for our Scalix installation because of the specific recommendations here that I do so. CentOS is rock-solid and stable, and I like it a lot. It is NOT as easy to config as Opensuse, but then, that's not something that you normally do every day with a mail server. You generally set those up and let 'em run.
Just my opinion, and worth precisely what you pay for it.