I've used Ubuntu for 1 year and Gentoo for around 3 years.
Now I'm using Debian on nearly all my computers for about 4 years. Stable on my servers and at work on my laptop, Sid on my personal laptops/desktops.
Stable is, well, stable (much more than RHEL/CentOS), the security fixes are published quite fast, and I've never seen an update breaking something on my servers. At one time I even put an auto update cron job every night on our dev' plateform without any issue.
Sid is, for an experimental distro, quite stable. The only annoying issue I had was with chromium crashing regularly for around 10 days until an update fix it.
There tooling is quite fun. At first it seams a little strange and old school but it's actually quite powerful. I'm thinking for example about reportbug. The first reaction is: WTF, a bug tracker system entirely based on emails..., the second is: whaou, it's powerful, it automatically recovers all the relevant information (architecture, version, dependancies, relevant log files), it gives you a list of other bugs that might be relevant, it automatically notifies the maintainer/group of maintainers in charge of the package... all this in a normalized and automated workflow.
And It's just on example, other part of their infrastructure are really nice (daily snapshot of their mirrors, rss feeds for security alerts, package searching though the web interface...)
Backports are also really nice.
And there are shit tons of packages available, including stuff many other distributions haven't included yet in their repositories (ex: grafana/influxdb).
Their packaging tooling is quite nice to.
The two things I dislike are isos without non-free firmware (even if non-free install iso does exist) and preseed which is painful to use and instrument to automate deployment (compared to kickstarts).