You probably want a mix of both, daily/hourly rates to give you stability, fixed cost to charge based on the value you provide instead of the time spent. With

You probably want a mix of both, daily/hourly rates to give you stability, fixed cost to charge based on the value you provide instead of the time spent. With fixed cost my hourly rates can easily be 3x normal rates but I'm also getting more risks (extra meetings or overtime, clients not paying).