I cook belly pork either quickly at a higher heat or slowly at a low heat. The first produces the best crackling IME - the latter produces a more tender, shreddable meat.
The best crackling requires double salting (salt, leave overnight uncovered in the fridge, rinse, pat dry, salt, pepper and oil before cooking).
When I slow cook, it tends to be with a lot herbs and/or spices... I usually end up shredding it or leaving leaving it whole but having it cold.