For home cooks that are just looking to make dinner, and not restaurant-quantity stock: bigger is not better. We recommend getting the smallest pressure cooker to fit your needs because a bigger the pressure cooker will take longer to reach pressure, will need more liquid to get there and it will be bulky to both clean and store.
More material - A larger pressure cooker will have more metal and that metal will take more time to heat up – time you’ll be waiting for it to reach pressure .
More liquid - As pressure cooker size increases so do the minimum liquid requirements – while a small 2qt pressure pan only needs about 1/2 cup of liquid (or less) to reach pressure a much larger 12qt pressure cooker needs two cups (or more)! The same piece of meat that braises in the smaller pressure cooker can only be boiled in the larger one - limiting the cooking techniques that can be achieved.
More work - On the more practical side of things, a giant pressure cooker is going to be tricky to wash and store. Depending on your sink and water tap configuration it can be quite a challenge to wash. Instead, a 6-quart cooker with a dish-washer safe base can easily slip into the bottom rack.