I price most of my design work out as packages. One service for one lump sum. The better I get at my job, the faster I can turn around quality work. That translates into higher hourly rates. But I rarely charge by the hour. Here's why: people aren't buying blocks of my time; clients buy my solutions to their problems. If they have no skill at all to design a logo for their business, but they want amazing results, they can't do it themselves. They need to hire a professional. They aren't spending money to save themselves the time they might have spent doing it on their own. They are spending money to hire someone to do something they themselves cannot do.
Another way to look at it is that if you get faster and faster at doing what you do over the course of your career, you would earn less and less each year if you charged hourly. By contrast, years of experience are worth something, and if you charge for the solution to their problem, not the time, then you can charge more and more the better you get at it.
So, are you charging for your time, or for something more valuable?