Media Design, The Netherlands
We are a webhosting provider that offers domain registration, shared hosting and dedicated servers. When we started in 2000 we chose Debian for various reasons, the most important one being that Debian's packaging system and tools were far superior to other distributions at the time.
Since then other distributions have caught up in that respect, but Debian remains our choice for dozens of servers (web, database, mail, DNS, etc) and a few desktops, both in the datacenter and at the office. Its reliability, maintainability, security support and licensing remain top-notch and ensure we can provide excellent quality to our customers.