The best time tracker you use

Hey, which software or online services do you use for tracking time as freelancers?

So far I have been using just a simple file with notes. However now I changes my work a little bit, and I'd like to send a nice pdf with detailed report.

I checked toggl, looks nice, however I need to write more detailed reports. When quite a simple task took like 2 hours, I'd like to provide detailed information about all the problems I found, and how I solved that.

So, what stuff do you use, and which should I avoid?