The Oster Classic 76 is the top-rated heavy duty professional hair trimmer of 2015, according to BestReviews.com. For lighter trimmers, BuzzCutGuide.com recommends the Oster Model 10, as of 2015.
The Oster Classic 76 Universal Motor Clipper is powerful and durable. It can cut through thick hair, but it doesn't heat up after long hours of use. In addition, most of its parts can be replaced or sent for repair. The only downsides are that it's louder, larger and heavier than most hair trimmers.
The Ostel Model 10 is a smaller trimmer, making it suitable for precise cuts. However, it's more expensive than the Oster Classic 76, and it's reported to heat up after heavy use.