How to choose the coating?
The inner coating is the most important thing when it comes to ease of cleaning and the longevity of the cooker. If the coating is good quality, your device can serve you for years to come, and you can be sure about the safety of the food cooked there.
Teflon coating is the most common coating for cheaper electric pressure cookers. It has the lowest coefficient of sliding friction, meaning that food will not stick to it. However, this coating is easy to scratch, and it will eventually crumble off in high temperatures. There's also an ongoing debate about how safe the non-stick coating is. If you plan on using a pressure cooker temporarily (e.g. just during the school year), or if you will only use it once in a while, a teflon coating will be okay.
Stainless steel coating is the most durable. It may be not quite as scratch-resistant or non-stick, but it is safe to use and will last the longest over constant use. Compared to aluminium or teflon, stainless steel is not as good at conducting heat, so it will take a little longer for the pressure cooker to warm up, but the advantages of this premium material far outweigh the disadvantages.
Aluminium coating is commonly used for stovetop pressure cookers. It is less expensive to make and lighter in weight than stainless steel. However, it's also less durable and may warp over time, which can compromise the safety of the pressure cooker. This is better for people who do not use their pressure cooker very frequently or who have more experience.