If you are essentially freelancing full time, consider changing your billing to daily or weekly rates anyway.
If you are doing highly specialized work that relies on experience & knowledge, do hourly, only for focused work, and bill high enough that your "slack" hours are covered anyway (e.g. target approx 1000hr/yr actual billed will cover your salary needs).
The "real" answer if you want the best return for your time is move to project level billing, not time, if you can with your clients.
Sometimes your clients will drive how you can bill anyway, of course.
If you are essentially freelancing full time, consider changing your billing to daily or weekly rates anyway.
If you are doing highly specialized work that relies on experience & knowledge, do hourly, only for focused work, and bill high enough that your "slack" hours are covered anyway (e.g. target approx 1000hr/yr actual billed will cover your salary needs).
The "real" answer if you want the best return for your time is move to project level billing, not time, if you can with your clients.
Sometimes your clients will drive how you can bill anyway, of course.