Per hour or per job, how should you charge?

As an independent consultant, do you prefer to get paid per hour or per job? What is fair to the client? I have started my career in IT doing jobs that paid per hour and eventually I started to work on my own and I started to charge per job.

I think charging per job is both fair to the client and to the consultant, the client shouldn’t have to worry about how long will it take to finish a job and the consultant should be paid based on his experience and his ability to finish the job.

I still remember when I first started to provide on-site service for wireless LAN setup, some of the equipments were new to me and it would take me hours to configure them but as I became more experienced with the equipments, my time on-site dropped significantly ,in both cases, I charged the client the same. It was not the client fault that I was slow and he shouldn’t have to pay me for time I have to spend getting familiar with new technology, but at the same time as I improved my speed, I should not have been paid per hour for jobs I can finish in mush less time.

One time I was working on client’s wireless network and I was able to finish the whole setup and less than an hour, so he was surprised and said to me “did I pay all that money for less than an hour of work”, so I replied to him “It took me hundreds of training hours to reach to this speed”.