For me it's a tie between Oracle, Atlassian, and Microsoft.
All three of them have built their business models around intentional poor design = money for extra services. They could make their software easier and more functional, but they intentionally don't so because it would hurt their profits. That kind of greed is inexcusable to me.
It especially sucks if your company migrated from a working but "unsupported" wiki system to Confluence, importing all the pages and breaking all the links in the process.