KVM is better. But let's just look at the software instead of judging.
Hyper-V was a free solution from Microsoft to virtualize Server or Client OS as it is a feature on Windows Server since 2008 and came in Windows 8 as well. Free because they had a special SKU dedicated for virtualization called Hyper-V-Server. It had a limited footprint through a core installation (no GUI) to minimize updates it would need.
But that was until the Windows Server 2019 release. With the new release line named "2022", they dropped that SKU altogether. Microsoft now proclaims you should use their Azure-Stack-HCI solution which is a paid offering with a subscription. That in itself is no bad thing as it would work pretty well (did not try myself but read about it). Alas, you will have to pay for that.
Another downside of Hyper-V is the management capabilities and requirements: You have to use Windows to manage that (which you probably already use anyway) but you have to use at minimum the same OS version your Hyper-V is running on. So if you have Hyper-V Server 2016 you have to use Windows 10 as a minimum (expect to have the same feature built as the server 1607).
On the other hand, there is KVM free on most (if not all) Linuxes. There are even free offerings like Proxmox VE with a full package to use it as an appliance, manage through a browser, and such. Way more straightforward than Hyper-V. Citrix Xen Server is also a great solution to get you started with virtualization.
Commercial solutions are also out there to deliver to more production-inclined needs. One is Nutanix AHV which uses KVM at its core. See my article about that for more information.Personally, I used KVM in private projects and some test scenarios at work. We use AHV at work and it is perfectly running there.
I also have a Hyper-V running with a few VMs for a small shop which works great. You have to settle with some limitations but I will switch that away from Hyper-V because of that mess they made with 2022 (I don't want to pay for a thing I have used for free after 10 years. besides said shop is a non-profit). I'm just waiting for the next hardware refresh.
So yes, I think KVM is better and not only because it is still free.
I would think a better comparison would be Red Hat Enterprise Virtualization (RHEV https://www.itcentralstation.com/products/rhev?tid=il-q) vs Proxmox VE.
However, I don’t have any experience with either of these two products or XenServer, as we use VMware internally.