As sophie said, there are lots of things that the water bath method can be used for. I wish I had a pressure canner (I gave mine away before I left Alaska). It would probably be pretty easy to do an online search, but there are a number of foods which are NOT recommended with the water bath method because they don't have enough natural acid (or sugar) to preserve them properly and bacteria can grow which you'd never ever see. Pumpkin, squash, applesauce, apple butters....off the top of my head aren't suggested by water bath method and those are the things I'd want to can.
Presto is by far the most reputable company as far as canners and pressure cookers are concerned. The seem to strive to keep replacement parts standardized and many hardware stores carry the parts as part of their normal stock. Presto makes the old aluminum variety and now have stainless avaliable in many sizes. The aluminum certainly wouldn't be touching the food so that's not a worry, but they get an old kind of look as they are used which I'm not fond of. I'd rather spend the extra and have the long lasting finish of stainless.
ETA-I think I would want to get the larger size, too. And, now that I'm thinking about it perhaps pumpkin and applesauce/butter aren't suggested in a pressure canner, either. That said, my grandmother probably did both with just a water bath and none of us ever died.
Exciting!