Buying a canner is an expensive proposition! One of the most popular classes I ever taught at a local preppers group (lots of eager newbies) was about canning, and many of the questions asked revolved around what to look for when purchasing canner to use as one of your major food processing tools. I thought we would be there all night (LOL) with people looking at my assorted canners and asking about the pros and cons of each kind.
Recently I have seen the "instant pots" mentioned in canning circles as another kind of canner. Nope, more like my decades old 4-qt pressure cooker. Mine is a stovetop version, which I prefer, because even without power I can still fire it up even over a campfire. It also has three pressure settings - 5, 10, and 15 pounds, and came with a rack so I could use it for water bath canning of small jars. When I got it as a wedding present, it was considered good for pressure canning as well, but recently researchers have found reasons to doubt it's ability to pressure can properly due to its small size and fast heating properties. It came with an excellent recipe book, and does what it was designed to do quite well - cooking foods in 1/3 the time, and tenderizing those really tough cuts of meat that are often all newlyweds (or college students, or other monetarily embarrassed people) can afford to buy much of. It also speeds up the cooking of legumes tremendously. Its cute, looks like a mini-canner. But for canning? Water-bath only, and small jars (half pints) only, so I use it only to can things like specialty condiments like jelly, mustard, and pickled jalapenos. It is much easier to lift, and fill, than the big canner so I do use if often.
OK, now about those big canners (7 quarts or more). The cute speckled blue ones with the cool jar rack inside are instantly appealing, especially as they are cheaper on initial purchase, often come with cool kits of tools like jar lifters and lid magnets, and do NOT have intimidating autoclave-like fittings that look complicated to use. They are easy to use - once you know how to boil water, you can make it work. However, they are somewhat limited. You can only can acidic foods in a boiling water canner (the blue speckled ones). That means, jellies, jams, fruits, and acidic sauces.
Although old canning books give boiling times for non-acid foods, and some old-timers do can that way, please do NOT try to can non-acid foods in a boiling water canner. The risk of deadly poisoning is very high, and you do not want to risk killing people (well, people you would be feeding anyway). The boiling times are extremely long (several hours in some cases) for those foods and keeping the canner working for extended times means you have to have several kettles (big ones) going at the same time to replenish boiled away water. And LOTS of water is heavy, and it is hot enough to make things risky. So save the boiling water canner for jellies, jams, pickles, and fruits.
Getter yet, if you only have room for ONE canner, spend the money on a pressure canner. You can remove the gasket (so there is no pressure build up) and it works like a boiling water canner.
A pressure canner is also the ONLY safe way to cook low acid foods (meats, vegetables, non-acid sauces, many main dishes, legumes & pulses) which if the canning bug bites you hard, you almost certainly will want to try. Being able to can as wide a variety of foods as possible is one thing that makes canning more than mindless labor. You control what goes, or does not go, in each jar, and you can make speciality foods according to taste or dietary restrictions that are MUCH healthier than the stuff in the stores.
Now for pressure canners, my recommendation is for a weighted gauge canner. Why? They are easy to use. You can listen for the sputter and know they are maintaining the proper pressure (while you can do something else, like filling more jars, or watching your favorite TV show). It is not as hard to adjust the heat level to keep the proper pressure, because a weighted gauge will release excess pressure if it gets too high. With a dial gauge, you have to keep an eye on it to get it up to the desired pressure, and watch it to make sure the pressure stays at the proper level. You also should get the gauge checked for accuracy (some places say annually). You can order a weighted gauge from www.pressurecooker-outlet.com to replace a dial gauge if you decide to change pressurizing systems. Many folks have done so and prefer the weights as well. Noisy they are, but for monitoring that is a good feature. So get the one without any dial on top.
Stainless steel or aluminum canner? Each has its adherents, but as I get older, I like the lighter weight of the aluminum canners. I also prefer the 16-quart size to the 23-quart size because it is less heavy and awkward to get on to the stove. (The quart size, btw is how much liquid the canner holds, not how many jars. The 23 quart canner holds 7 quarts or 20 pints of regular jars; the 16 quart holds 7 quarts or 10 pints.) Most of my canning is in quart jars, so I bought the smaller one. If most of your canning is in pint jars, the 23-quart canners have two racks so you can stack in twice as many. It might be worth the extra weight for you, it isn't for me. I have purchased an extra rack for my smaller canner though, so I can stack in half-pints if I want to.
Gasketed, or steel to steel seals? Price aside (steel to steel is more expensive) and aside from the fact that I can't find a steel to steel sealing canner without a dial gauge, I still like the gasket sealers a bit better. Metal pan rims can get dented and I feel that could compromise a steel to steel closure's seal. A gasket would just expand to fit the kind of wear dents I seem to see on older canners. Especially on aluminum ones.
What about parts? Since I like gasketed pressure cookers, I ordered a spare gasket from www.pressurecooker-outlet.com, and that is where I got my extra rack. I also got extra weights for the pressure gauge (they have a way of getting lost in my tool drawer until canning season ends, LOL, so it is less stressful to have a spare).
Recipes are all over the internet for canning. The USDA guide or Ball's Blue Book are the gold standard canning guides, and with them you can put up a huge variety of foods. Stews? Meatballs? Pasta Sauce? Chili Beans? Beanie-weenies? Mock Smoked Fish? Pickled Eggs? Yep. And that is just the "normal" things you can put in jars. If you want to get more exotic, try canning cheese, butter or bacon (crisp or soft, your choice). Get a sealer and you can "dry can" by vacuum sealing dried foods in any spare jars; or you can throw in a couple oxygen absorbers to pull a vacuum. Canning is VERY versatile.
Canners don't "blow up" anymore because they have safety fuses/plugs put in, that pop out like a cork if the pressure goes crazy. I had that happen to me - once in 35 years - there was no ka-boom, no food splattered all over the kitchen, nothing but a pop and a loud hiss as it de-pressurized. The jars broke inside the canner, so that batch of food was tossed out, the canner washed, the vent tube cleaned out, and the next morning I went to the hardware store and replaced the screw-in safety plug. (You might want to order a spare, and spare gasket, because not all hardware stores, even rural ones, have canning supplies like they used to.) You probably won't even need it - I was doing a no-no by canning pureed pumpkin instead of cubes, and the vent tube got blocked when the pressure forced some out of the jar. My bad. Won't do THAT again. I was more aggravated about having to do the batch over (the RIGHT WAY) and losing those jars than having to replace the pressure plug though.
So don't fear the canner....just get one you can handle, for the purpose you intend, and you will find you can become a canning fan! Me, I'm an addict.