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In some environments, there is only one option: RHEL.
For example, if you want to cluster anything besides Oracle on EMC storage solutions, the only option is RHEL2.1 (at present). If you *are* doing Oracle clustering, then you can use SLES8 too if you want. (And, no, Debian is not listed, the only two Linux distributions listed at all are RHEL2.1 - x86 and ia64 - and SLES8 x86).
Once you've paid the money for the EMC box, the cost of RHEL licenses is peanuts.
If you don't have certification reqruirements, I don't see why you would want the pain of RHEL ... and all the RHEL clones give you just that, the pain of RHEL without any of the advantages.