BST wise, it is a tie of 580 BST:
Zapdos, Moltres, Articuno, Entei, Raikou, Suicune, Regice, Registeel, Regirock, Uxie, Azelf, Mesprit, Cobalion, Keldeo, Virizion, Terrakion.
All of them have their competitive uses, but none of them is particularly bad. The worst legendary is Regigigas. Sure, it might have 670 BST, but that awful ability allows it to get pretty screwed over unless you magically get rid of it.