When buying a pot rack, most people pay the most attention to the overall design of the rack itself, however it's a good idea to take note of the hooks on the rack as well, and make sure they'll serve the purpose you require them to.
The primary thing you want to decide is whether the hooks on the pot rack you're getting are strong enough to hold your pots and pans. If you have a cast iron set of kitchenware, you'll need thicker and stronger hooks to support the weight, whereas if your pots and pans are made of aluminum or stainless steel, you can get away with smaller hooks.
Along the same lines as strength, you want to make sure the hooks are large enough to fit your pots and pans on. Many pots and pans have hanging hooks made of a relatively thin piece of metal, you can get smaller hooks to match, but if your kitchenware has holes through the handles themselves, the hooks would need to drop down enough for you to fit your pots and pans on them.
The final thing you want to look for is if the pot rack has enough hooks to hang all your kitchenware on. Nothing is worse than having a single pot that won't fit on the rack with the rest of the set.