What hardware is recommended?

For IOMMU groupings, modern (x99+) Intel chipsets work nearly flawlessly. Modern (A300+) AMD chipsets work similarly well.

If you are planning on passing a GPU to a guest, and are using a CPU that lacks integrated graphics (without onboard video), the common recommendation is an Nvidia gt710, which is single slot, passively cooled, and can easily be picked up for less than $60 USD.

For KVMs, the only model that is really recommended is available for both single monitor and dual monitor