I use XenServer since 2009. In 2008 i compared Hyper-V, VMware and XenServer for about 6 months (only the free versions) and my winner was XenServer. Not only because I am a fan of Open Source I choosed XenServer. My primary focus was performance and usability (for admins). VMware was too slow on low end hardware like HP ML110 and Hyper-V needed an AD. So I stayed with XenServer.
Since XenServer 7.3 I looked for alternatives and found the XCP-ng project.
I have a small IT company with 3 employees. We serve small and medium-sized customers. Unlike other IT companies around here, we use a lot of open source to offer alternatives to our customers. About one week ago I tested Xen Orchestra (compiled from source) and I like it a lot. I miss some features, but maybe I have not discovered them yet.
If you have plans to support other languages in Xen Orchestra, I can assist you with the german version.