Depends on the application (what you're using it for) and resources (who is using it). I actually use several depending on the client, engagement, and complexity.
- For smaller initiatives, I'll use Gantter with Google Docs. Very easy to use for small teams and works great for sharing & linking to docs.
- For some clients, they prefer MS Project so I'll use it to simplify rollups for PMOs (aggregate reporting).
- For agile projects, I'll often fall back on Assana & Jira (issue tracking) as it's very inexpensive and provides solid support for agile/SAFe methodologies with stats for teams and you can integrate it with build management (DevOps configurations). [there are a bazillion agile tools on the market, so pick one you like]
- For small to medium sized organizations, I'll introduce Workfront (Saas-based tool) to simplify deployment and it's a low cost and easy to train solution.
- For large organizations (most already have something, but if they are looking for more robust tools I'll go with a PlanView because of the integration with budgets and ERP systems. ( I have deployed Project Enterprise from MS - lot of work, lot of training )
- For large organizations looking for a more advanced set of portfolio capabilities, I'll introduce Planisware (built on a Lisp platform) since it's extremely flexible, has great visualizations, and has built-in connectors to AllegroGraph (graph repository).