i really really love
often referred to as Vegetable Cheese, yes it smells weird (like a baby's diaper) but it's really tasty, has a good pack of protein and minerals, and since it's fermented (like miso and soy sauce and tempeh), it is believed by some to be the better type of soy to eat; its like durian, an acquired taste, for sure. plus it's got that sticky stuff like okra (kinda looks like snot). but it tastes great. i been eating it for years because my wife is from japan. and if you cook it, the smell and the snot lessens (ie with spaghetti, deep fried, as a burger).
main thing is get it non-gmo (and/or organic). what brand? put it this way i've never had a natto i didn't like! several brands i have are the "good" natto, another one has picture of a mountain, one has a grandmother cartoon, a fake wood container, also i've had homemade by a friend that was the best. i don't know the names because the writings in Japanese so i just read the English label that's stuck on the box (usually it's produced and/ or imported by Nishimoto or JFC).
but be beware: it usually comes with a sauce packet that is usually like dashi (fish flavored soy sauce) so i'd mix it with your own known good soy sauce, ketchup or mustard. plus if you order it out make sure it wasn't made with that dashi (also sometimes they mix it with raw egg when they serve it in restaurants).
where to find it? either a Japanese supermarket like Mitsuwa (in NJ and Cali) or a good Chinese supermarket that has other Asian foods, too. i guess i'm fortunate to be here in NYC we have 2 excellent veg friendly Chinatowns plus quite a few Japanese markets to choose from. if you are in the sticks and can't find a place to buy it you may be able to make it by buying the natto culture itself (Bacillus Natto, never tried that myself).
interesting side note there is a remedy for heart and vascular disease called nattokinase which is from... NATTO!