I have 2 x Intel NUC6i5SYH that run as ESXi 6.5 hosts. They each have an Intel Core i5-6260U processor (2 core, 1.8GHz) and 32GB RAM. Each has a 250GB Samsung 850 EVO M.2 SSD and a 500GB Samsung 850 EVO 2.5" SATA SSD There is one onboard 10/100/1000 network interface, as well as a USB attached 2-port 1Gb NIC.
In addition to those, I also run an Intel NUC Skull Canyon as my main workstation. It has a 4 core Intel i7 processor, 32GB RAM, and runs Windows 10. VMware Workstation runs on this as well and is where I have my domain controller, vCenter, and one or 2 other VMs.
External storage is handled by a Synology 1515+ with 8TB usable. It serves NFS and iSCSI storage to the ESXi hosts.
All of this is connected by a Cisco SG200 8 port Gigabit Smart Switch.
Overall I'm happy with this setup, although the NUC's don't have a few features which I'd like such as IPMI or 10GbE. However, it is very quiet and doesn't consume that much power.