Both have their advantages. Therefore it comes down to, as always, the area of application. Do you need footwear which will remain waterproof for a long period of time? Do you need a boot or shoe which prevents rain from penetrating? Are you looking for footwear which you do not need to repeatedly and regularly treat to make water repellent, for example, on long trekking or alpine trips? Many people consider leather to be the more natural option and as always comfortable to wear. For normal areas of application the impermeability of leather is more than sufficient, that is, if you take correct care of it! In this sense neither is better, the best material for your footwear depends on your personal preference and your planned activity.