The strongest fat burners are called 'Thermogenic Fat Burners', used to help raise metabolism. A faster metabolism burns more calories. The more calories you use, the more likely it is the body will burn body fat to provide the calories. By raising metabolism, thermogenic fat burners may also raise energy (which may help motivation).
Thermogenics are also used as pre workout, or pre event supplements. They may be useful to break through barriers. Another approach is to use 'Fat Transporters' (called L-Carnitine or Carnitine). Carnitine may transport fats from body fat stores into the muscle cells for burning.
For fastest fat loss help, a popular way is to use a thermogenic fat burner and a Carnitine at the same time.