If faster cooking is the top priority for you, then definitely the pressure cooker. It cooks in about a third of the time.
I prefer the slow cooker, because I can just throw everything in it in the morning, go off to work, and when I come home dinner's just about ready for me and the house smells GREAT.
Taste wise, meats will be juicier and more tender when slow cooked.
Maybe you could borrow one of each from a friend and test them before buying.