For poultry broth, I used to use mostly cheap boney bits like chicken backs and turkey necks, but now I hardly ever find them at the stores.
Now, for the most part, I just save bones from whatever else I'm making in a large freezer bag until I have enough to make a batch of broth... or, if I'm out of broth, I'll buy whatever bone-on chicken is cheap - usually leg quarters.
For beef broth, I buy the big "knuckle bones". They're about $7.00 for a pair, but I get a lot of rich broth out of them, plus lots of TALLOW.
That's another bonus of making your broth - delicious fat to cook with. For really awesome beef broth: roast the bones for an hour in the oven after covering them with a few Tbsp of tomato paste. Dump the whole mess into the crock pot, including all the juices and drippings, cover with water, let 'er rip.
I hate drinking broth. That said, it makes a lot of other stuff taste awesome: my soups, sauces, stir fries, etc; and I do believe in the health benefits because I don't otherwise get nearly enough collagen or gelatin.
I do find it tastes better in the Instant Pot. Pressure cooking just adds so much depth of flavour. Save up for one. Don't wait for your crock pot to die, it probably won't. My mom died before her crock pot did and she had it before I was born.
When you pressure cook, you need to have at least 1 cup of liquid to create the steam, and this is probably one of my more common ways to use the broth. It infuses a lot of flavour, then makes a fabulous sauce or gravy.
It used to be suggested that you add vinegar to the broth so that by acidifying it, you draw out more minerals. I don't bother anymore; I'm pretty sure it was on Mark Sisson's site that that was debunked. The bones often crumble after I've made the broth, so that indicates to me that the minerals are gone (and into your broth.) If you choose to add vinegar, you won't taste it afterward, at least in my experience. I hate vinegar, so I wouldn't have done it if I could taste it.