I'm in the process of replacing TeamCity with Azure Pipelines (not my choice). It's ok but I also doubt it's best in class, TeamCity is far better IMO (more flexible, more informations/actions on one screen, less clicks, better logs display, better tests results display, live tests results, etc). I wish they had an hosted offer, and yaml configuration.

Can't find the discussion now on GitLab, but I recall comments claiming that Azure Pipelines is very flexible, and GitLab CI's new task DAG should be modeled after that.