I haven't noticed any downtime either -- all my downtime has been my own doing -- I only run a few small sites and periodically staging versions of client applications so I don't have a crazy amount of load.
I've been using Hetzner for roughly 2 years and am a pretty happy customer.
I can say though that the latency is pretty bad when compared to local options -- their server are pretty geographically far from where I and others who use some of my apps access from, and I get ~200ms of latency that I can't do much about. I've looked a traceroute and it's not their network but rather some points in between.
In the past two years, I remember they have done scheduled infrastructure maintenance twice and unscheduled interruption for a few hours. So, no, it's not 100%. But, AWS has also had some interruptions. From personal experience, this Hetzner downtime has simply been negligible enough. Bigger issue have been replacing commodity memory a few times, which could have been avoided by paying a few more dollars for more quality.