First-Root is a provider for VPS, domains and web hosting based in Düsseldorf (Germany).
As far as I remember, I became aware of First-Root via a forum - from the beginning I was very satisfied with the VPS there; I was a customer there from 10/28/2012 until 01/09/2014.
I have to say that the customer support was especially positive, as it answered very quickly even at impossible times. I was also very satisfied with the performance there, so I booked several VPS packages there in the meantime.
What made me leave were technical problems, because apparently a PHP script from me could trigger a bug in the OpenVZ virtualization software after a few hours of running - and the host was shot down (sic!). However, I could not do without this script at that time. At that time there were also some other unfortunate failures (hardware failures) for the company, which is why hosting there was no longer an option for me.
At that time this was the only vendor I knew who also offered VPS based on the Kernel Virtual Machine. But I never tested this; I have an unfavourable package distribution (in the sense of CPU/RAM/HDD) in mind.