Hi,
I can recommend a Intel NUC, esp. NUC6CAYH.
I’ve used a PI2 and changed to the NUC some weeks ago.
I measured the power consumption with around 6 Watts (OH2 and some other services, 4GB, idle, no monitor)
The box is equipped with a fan, but you can easily configure it in the bios to stop when idle.
Pros over the PI are more CPU Power, much more RAM and the easy addition of a SSD.
Con is the price, around 170 EUR here, plus somewhat 30 EURs for 4 GB memory (DDR3L I think, I had some lying around here)
I’m running Ubuntu Server 16.04.2 LTS.
OH2 can be set up with the great openhabian in no time.
Peter