How about a electric shaver.

Straight edge razors and scissors are also good tools to employ. I really don't think there is one tool that is best over another and you need to employ them all just as a good barber or hair dresser would.
One thing I would say about the electric shaver, is that it works best not to try and take off a lot at one time. In fact just like a barber you would want to get the most of your fur off with a pair of scissors and then use the shaver to finish and clean things up. A comb or brush is also a good tool to have to get your fur to stand up so you can get to it to cut. For example if you wanted to shorten the fur around the muzzle of an animal but then have the longer hair blend in nicely you would want to use your comb or brush to raise the hair in the muzzles area and then push away or separate the hair that you want to stay long to blend in. Ok that all makes sense in my head let's hope it translates to word.
