I've worked with several network device vendors in my 10+ years of being in the industry and my favorite continues to be Cisco IOS. Overall, Cisco IOS tends to be the most stable, the most intuitive, has the best TAC support, and has the best knowledge base articles and white papers.
We use it for every linux service we need to have running. It really works great and is easily manageable with the SUSE Manager, which helps a lot with the updating process. Although it is not stressfull on the CMD itself, it really does simplify things. Besides that, we are really happy with working with SUSE Linux Enterprise Server.
By this point, there are several "flavors" of the Cisco IOS such as XE, XR, and the standard Cisco IOS. While they are all fairly similar, there does exist syntax differences between them. It would be ideal if at some point in the future, Cisco is able to unify all of them into one standard operating system which would use the same syntax across all platforms.
While overall Cisco does a great job of QA'ing their IOS, no matter the release, there's always some minor bugs. I think it's important that Cisco continue to pour resources into their QA team to test their software.
While I'm very familiar with the graphical readouts of "show processes cpu history" I would love for Cisco to eventually find a more intuitive way to display this data. I can't begin to count how many times I've had to teach more entry level (and even mid level) engineers how this graph is interpreted.
I do wish that Cisco had something similar to Juniper's "commit check" or "commit confirmed". This helps validate the changes you're about to apply, and catch errors, so that you have a better idea of the impact of the change.
The support window for service packs after a new SP is released is too short.
Community engagement is low.
There are times when supported packages fall too far behind and create compatibility issues with applications. The Open Build Service usually provides a way around this, though.
The data that Cisco IOS is able to provide is extremely relevant, it's fast, and it's intuitive. I also love that you're able to leverage things like macros or EEM scrips to run multiple commands at once. This is especially useful when you have more junior or entry level engineers in your environment and you want to provide them with a "shortcut" by having them type a single command to execute multiple commands.
We've been using this OS for about 8 years in a productive environment. During this time, we have never run into any problems that stopped or impacted our production environment. We have been able to solve any problem we ran into using either common sense, suse documentation or suse support.
Support personnel are helpful and fairly fast to bring resolution to non-emergency issues. Patches are created and posted in a timely fashion. We so far have not had any major problems that needed support
We have found other Cisco software to be filled with added functionalities as compared to iOS. New NCS software has certain programmability features that are advantageous to legacy iOS software but are more complex to use for some users. Hence, we still have most areas of the network that functions using iOS software.
We went straight to SLES when we initially started migrating oracle to hana since at that time, HANA came on a pre-installed server that had to be purchased from an official vendor, and SLES was the only allowed OS. We stuck with SLES after we became certified to do our own installations because so far, SLES was a good fit for us.