Second Proxmox. While our footprint is likely much smaller than many of the other folks on here, it's been a life saver for managing LXCs.
Proxmox has been solid and near problem free for our simple deployment
As far as Linux system containers go, is the landscape still raw LXC, LXD, and Proxmox?
LXD snap had caused some issues for me. I didn't have any issues with it when it was packaged as a distribution package. Plus I briefly considered it again when VM management came out, but Proxmox still won over it.
There's also Nomad which has an LXC plugin alongside all the others.