Never charge by the hour, as it gives a ceiling to your potential earnings. Charge by the job/retainer/etc and then spend a lot of energy becoming more efficient.
But beware you take on a ton of risk, especially as complexity and size of project grows. Many clients will also divide the price by how many hours they think you’re working and still think in hourly terms...
Different billing schemes are appropriate for different projects and clients.
"Time and materials" billing is totally appropriate if the two parties trust each other and the nature of the project is open-ended or loose about the deliverable.