Intended to safely preserve low-acid foods (like vegetables and meats) in jars, pressure canners may all look and function similarly, but the best pressure canners will be constructed from high-quality aluminum that's safe for use on your stovetop. Which model you choose will ultimately come down to your capacity and budget needs, as well as which pressure gauge style you prefer.
When you are trying to determine what size pressure canner to get, think about how many batches of food you intend to preserve at any given time and your preferred jar size. A good starting place for batch canning for most people will be a 20 to 25-quart model.
Depending on your recipe, you'll need to adjust the pounds of pressure (PSI) accordingly, and there are two types of gauges to consider. A weighted gauge is the most straightforward and accurate— there's typically only three PSIs to choose from (either 5, 10, or 15), and you place the one you need right on the regulator. It will then alert you with a jiggling noise when it's reached the respective pressure.
A dial gauge lets you turn a knob to the exact PSI you need, giving you the flexibility to choose any odd number. Though it's easy to read, it's also more high maintenance— it will need be tested by a professional every year to ensure it's still registering the correct pressure.
Most pressure canners are made from heavy-gauge aluminum, which is a good conductor of heat. When it comes to locking mechanisms, however, a twist-lock model with a rubberized gasket is usually more affordable, but you'll want to keep in mind that the gasket should be replaced every three to five years.
Before making your purchase, you'll want to double check the recommendations from your stovetop's manufacturer to find out if a pressure canner is safe to use. In particular, smooth or glass cooktops have the most precautions.