Mode is a permission decision
A suggestion inside one file has a small action surface. An agent with terminal and repository access can explore, edit, and verify across the project. Choose the mode by the work the system must perform, not by which button feels more powerful.
Context should earn its place
More context is not automatically better. Include interfaces, tests, local conventions, and errors that constrain the change. Avoid attaching entire folders when a contract and two call sites explain the problem.
Use the lightest capable path
Fast models are useful for mechanical work; deeper reasoning pays off when requirements conflict or architecture is uncertain. The right choice is the least expensive path that still produces a result you can verify.