Not sure what you need, so I will run the gamut.

The best yogurt is one you make yourself with a good culture. Other than that, stay clear of high sugar commercial yogurts. Get plain organic yogurt, preferably from grass fed cattle, and then add your own goodies - berries, nuts, etc. Kombucha is too stout for me. A person can make kombucha themselves as well. I drink Kevita - mostly the ginger lemon one. It has been good for my digestion.

Mostly any fermented product you can make yourself with good ingredients is best. Store bought needs to be as clean and low sugar as possible. Almost any kind of cultured food is beneficial for regular use. Peoples around the world have used fermented products of all kinds as a mainstay of their diets all throughout history. In my experience however, most Americans just do not have an appetite for fermented foods - to their own determent. Anyone that is taking prescription medications needs to be on some kind of regular probiotic. Our lifestyles and diets are killing us.

If the gut must be turned around because of an acute major shift, like after antibiotics or major surgery, probiotic supplements are needed in higher doses. With serious gut problems, like C-diff, a fecal transplant from a healthy person has shown good results. There is also some research taking place on treating autism with fecal transplant. Some of the results are hopeful and impressive. There are high potency probiotic supplements for these more acute situations. They can be on the pricey side, but when you need that kind of help, they are useful. They key is to get at a minimum over 100 billion CFU. Here are some I have used and recommended with good results. An acute shift of the gut biome will not revert on its own - there must be an intervention of guided repopulation to return to a healthier state.

For more chronic digestive issues like Crohns and IBS: https://www.visbiome.com/

For after antibiotic use, taking several caps for a week or so and then 1 a day till symptoms subside. https://www.gardenoflife.com/products/our-probiotics/raw-probiotics-ultimate-care-shelf-stable-vegetarian-capsules

https://www.gardenoflife.com/products/our-probiotics/raw-probiotics-5-day-max-care-powder-banana

People often assume that just because they do not appear to have a gut problem that one does not exist. Just like the jabs, people often do not link their non gut issues to their gut. Research is showing that the jabs severely alter gut flora. This fact explains a great deal about some the underlying causation of the after effects from the jabs that we are seeing. I am waiting for these researchers to also find a link between severely altered gut biome and any vaxxine - which may be part of the autism link. Overall health is linked to healthy biome populations. Probably only about 1 percent of the biome in the gut has been identified. The rest.... well....we are still looking. But what we have found out so far is eye opening.