The way I look at it it's pretty much between Redhat, Suse, Debian, and maybe even Slackware.
It all realy depends on the attitudes of the management how much leyway they give the adminstrators. What sort of requirements they have and such.
For instance Redhat has the best support as far as third party applications and such go. If you require some sort of CAD software or specialized database application and those are from commercial companies and they certify specific Linux configurations those specific Linux configurations will include a Redhat operating system almost without exception.
Same thing with hardware certifications and driver certifications.
As far as Redhat themselves I've noticed that they tend to be at the for-front for enterprise level stuff. Things like clustering... They have their clustering suite with applications, kernels, file systems, and such for working with SANs and database clustering, high aviability clustering, load balancing clustering, and such. They have some interesting things such as a open source LDAP server and management suite that doesn't involve OpenLDAP. Things like that.
The downsides for Redhat is that they don't seem to be able to provide the same level of support that Unix users are accustom to. That is that with traditional Unix vendors like HP or IBM they have a lot of staff and a lot of support.. comparatively Redhat doesn't have nearly so much resources, although the price for it is comparative.
Now with Suse the best thing I figure they have going for them is that they are now owned by Novell. If you want to deploy Linux desktops and aren't sure about the best way to do it then Novell probably is your best bet. They have a LOT of enterprise Windows desktop experiance (compatatively) and are gaining good Linux desktop experiance. Scripts, network services, etc etc. Everything you need to gradually migrate to whatever you want.
Now for my personal preference it wouldn't be Ubuntu nessicarially, but Debian. I am of the opinion that as far as server systems go they should just be bare minimum. No gui, no nothing. Just the services that they need to be running and that's it. You should be able to remotely manage everything, even installations. You only need to touch the computer when something goes wrong.
For desktop systems I figure the best way is to go with just what people need to get their job done. It should be flexible enough that as the users grow and understand the system they could start to exploit it for their own purposes (like for example how people tend to 'abuse' excell spreadsheets or heavily use marcos.. these things are _potentionally_ good things as long as the software is designed to be flexible enough to handle it.). Also I want to be able to write a nice documentent on how to use Email or how to use the browser or find this share or that resources. I want to be able to print that out, give it to the users, file it under documentation and I want that to be valid not only next week, but 8 months later, and hopefully 2 years later. That users can file it away in some drawer and then look at it later and actually it still works. This is because I am lazy, but I figure Debian stable would be the way to most easily accomplish these goals.
Generally speaking boring is good.
But that's just me. Everybody is different with different goals and requirements. The way I figure it is that if you want to 'learn' linux the best way is to understand how it works, not nessicarially to understand how to use the configuration utilities and such.