Or are they all pretty much the same? While you're at it, what are your favorite things to put in a stock pot (beside the standard onions, carrots, etc.)?
It needs to be durable, definitely NOT non stick, and large enough to hold all the stuff you're going to put in. I always laugh when I see sets with a 5 or 6-quart "stock pot." No way you can make stock in a pot that size. Altho it's fine for heating up the finished soup.
I look for a thick bottom and sides and tight fitting lid. Cheap pots warp easily. As to aromatics, it really depends on what you are making. I like to use leek tops rather than parsley before I fill the bouquet and tie it up.
I have an All-Clad stockpot that I love. It has a removable basket that easily separates the stock from the chicken carcass and vegetables - nice feature if you can get it. Think about size of your family also, how much stock do you really need at any given moment. I make stock all the time and store it in used yogurt containers (about 2 cups). This works out really well for most of my needs. When I make chicken stock I use the carcass from a chicken I've roasted the day before. Add to that a couple of leeks, mushrooms, a bunch of carrots, and herbs. My favorite are bay laurel, flat leaf parsley, marjoram, and thyme. Garlic, peppercorns, and salt to taste. For vegetable stock I like parsnips, carrots, leeks, mushrooms, fennel bulb, and onions. I like bay leaf, flat leaf parsley, marjoram, and thyme. Garlic, peppercorns, and salt to taste. Just like with the chicken stock. You may also add tomato paste for added flavor. Simmer the chicken stock for 4-6 hours. The vegetable stock for 2-3 hours. Enjoy!
Thick bottom and large are your two major needs.