these two are the most commonly asked questions within bullous diseases.
the major difference you need to know is
pemphigus vulgaris- bullae are suprabasal. hence these are not tense and rupture easily..not very common in a clinical case for you to find a bulla
bullous pemphigoid- bullae are subepidermal..and hence tense.
a mnemonic..like a bull..bullae in Bullous pemphigoid are tough and stronger