Fizzy milk.
No thanks. I have no intention of learning to like it. I do like yoghurt, it's mostly the fizziness that puts me off kefir.
Kimchi and sauerkraut, on the other hand, I could eat by the bucketful. I quite like kombucha as well.
A couple of people have alread said upthread that the best way to support your gut microbiome is to eat a healthy, varied diet ("eat a rainbow" as they say) with lots of fibre. This is exactly right. Gut bugs feed on fibre.
It's still a developing area of science but there's a lot of evidence these days to support the importance of healthy gut flora, with proven links to other aspects of health seemingly unconnected with the gut (eg depression, joint inflammation, skin allergies).
I think the jury is out on probiotic supplements though*, and on the supposed health benefits of things like kefir and kombucha. I know in some countries they prescribe kefir following a course of antibiotics to help replenish gut microbes, but drinking a daily dose of fizzy milk won't do you any good if you live off Coco Pops and KFC.
*as ian said, the acid in your stomach will kill most of the bugs in your food, which is a really, really good thing on the whole, and probably one of the main reasons the human race didn't die out hundreds of thousands of years ago