With the deprecation of a majority of the services in macOS Server I am looking at moving at least part of our company server infrastructure over to Linux Server.
We have been more than happy with macOS Server (or OS X Server as it was) since we migrated to it from Windows Server several years ago but it seems now may be the time for us to begin the migration across to Linux Server.
We've had some openSUSE VM's running to provide a few services since around 2011/2012; I chose openSUSE/SUSE mainly because of YaST as I had limited Linux knowledge. Transitioning to macOS Server has allowed me to learn more about the open source packages that comprise macOS Server and gain knowledge of *nix command line.
We have also used Vyatta (VyOS) since around 2010.

Now that we will be migrating more services I am looking to choose a Linux Server distribution that we can rely on comfortably. I have read several articles about choosing a distribution but thought I would ask the Linux Server community here for some specific recommendations.

Mainly we need to run Web (Apache), Mail (Postfix/Dovecot), DNS, MySQL and Xojo Web Apps. Potentially we will also want to run FTP (or SFTP), VPN (OpenVPN) and Jabber.

I have looked at CentOS and RHEL, both of which seem similar enough to openSUSE that I have used before. I have also looked at pricing for SLES.

Is there any great benefit to paying for an RHEL or SLES subscription or is using openSUSE or CentOS comparable?

Additionally, is there any difference between Oracle Linux (which seems to be repackaged RHEL but they don't charge a subscription for updates only for support) compared to RHEL?

Any advice would be gratefully received.

The main benefit of SLES/RHEL is that you have someone to call if things go wrong. If you're in a smaller environment, and are comfortable doing your own admin/troubleshooting, you shouldn't have a problem. RHEL/SLES comes in real handy when you *NEED* verified hardware support, software support, etc., to avoid finger-pointing at dark O thirty when something dies. Oracle is a great example...you can purchase Oracle, and have it run just FINE on CentOS; but it used to be that if you called for support, they'd say "Well, you're not in a supported configuration, sorry...". Don't know if that's the case any longer for CentOS, but it used to be.
OEL is RHEL, but optimized for Oracle performance. While you CAN load it freely (like you can with RHEL), not paying for it isn't a good idea. Load CentOS instead.

Personally, I have servers running openSUSE with zero problems, and I'm sure folks here use many distros for the same things. If you're comfortable with openSUSE, there's no real reason not to stick with it. The services you've mentioned aren't hard to set up, and I'm running openVPN, Jabber, MySQL, Apache, DNSmasq, and SSH on CentOS and openSUSE. No problems with any of it. I'd avoid FTP like the plague...FAR to insecure. You mention a mail server...which can be daunting, unless you're just looking for some sort of relay to an upstream server.

The main benefit to SLES, RHEL and OEL is you have get support from the folks that created the distro.

I'd strongly advise AGAINST OEL as any Oracle product is apt to bite you in the end. Their licensing/support models are cost prohibitive AND they like to audit all the their customers every year which at best is an intrusion and at worst can end up costing you as they change their model to maximize revenues.

Most commercial packages (including Oracle DB and Apps) are built for RHEL and its derivatives. One reason to use RHEL is because you're more apt to find qualified candidates in hiring that have already worked on RHEL elsewhere.

CentOS is a binary compile of RHEL source so can be used for nearly anything RHEL is. The downside is that you can't get direct support from RedHat (although RedHat now maintains the CentOS project). A lot of the RHEL documentation is proprietary so to access it they require you to login which requires a subscription.

I haven't really used Suse/SLES but it appears to be the number 2 commercial distribution.

A lot of folks use Ubuntu both for personal use and in some companies.

Most of the requirements you listed are pure OpenSource packages so would likely run well on any distro so it comes down to a question of support.

By the way MySQL became part of Oracle when they bought Sun. They let go of or alienated a lot of the MySQL folks so MariaDB was forked from MySQL and has a lot more active development going on. You might want to consider using MariaDB instead. Many of the distros ship that instead of MySQL now.

Debian is also an option. I find Debian & derivatives much easier to work with than RHEL and the like. You can get support for it from various places online if you look, albeit not from Debian itself. Ubuntu also has support contracts. They work with companies like Walmart & Tmobile. I use it at home (not the same as enterprise) and have zero difficulties that aren't of my own creation.

Many Thanks for the replies.

The main reason I was looking, potentially not to stick with SUSE/openSUSE was that in the past we have done minimal installs, and then when installing some packages, inc Tomcat, it says it conflicts with "minimal base conflicts" which when uninstalled installs a lot more packages, which seems counter intuitive.

We looked at Ubuntu a while ago but I didn't seem to get on very well with it unlike SUSE.

Sounds like all of the distro's are much of a muchness. I'll have to start firing up some VMs and seeing what happens.