Packhounds have more general utility in both PvP and PvE. They are great at ignoring point defense modules, but move slower than normal seekers, and generate a fair amount of heat if you get real trigger happy.
Torpedoes are a specialist weapon, that are very hit or miss. Anytime you see torpedoes in PvP, they're going to be engineered with Reverberating Cascade, which can disable a ships shield generator by damaging it directly. The problem is, they're very slow, and experienced players are often going to avoid them with ease. Most ships can outrun them, as they only travel at 250 m/s.
I'd advise against using torpedoes in PvE, as you're very limited in terms of ammo, and NPCs are weak enough to be killed with conventional weapons.