Whiteboard
It ideally starts with good requirements before we hit the whiteboard. But I feel whiteboarding builds discussion and collaboration. It solidifies understanding and is cheap and quick. We all whiteboard. There's good work there.
Design Tools
I let my audience dictate levels of fidelity. There are stakeholders who remain engaged if artwork has higher fidelity. So I adapt my output to meet the stakeholders to successfully sell the design. I like Photoshop, Sketch and XD. I move quick. I use color and good, solid layout to sell efficient workflows.
Prototype
Using the right prototyping tool within the enterprise yields quick, testable assets. I quickly drive home both interactive flows, and transitions. Stakeholders and users remain engaged and invested with a solid prototype that solves their problem.