Proxmox is good with the large exception of high speed interconnects.

If I have Mellanox IB cards in my servers, proxmox fails to handle ipoib without a lot of legwork. Compare that to something like oVirt; that supports it out of the box.

There is very little incentive for me to recommend a proxmox subscription to any of my clients because having >= 40 gbit interconnects is far better than using lags on single gbit. High traffic internal applications, (and migration!) benefit so much from those interconnects.