Pro-biotics in pill form are dubious at best. Even yogurts available in stores have been pasteurized for longer shelf life (not to speak of the loads of sugar added). Vegetables from the cruciferous family, like cabbage, broccoli, cauliflower, and home-fermented yogurt will give you the most bang for the buck. Fermented forms of cabbage like sauerkraut and kimchi are supposed to be especially good for your gut bacteria.

I got lucky and the first kind I used worked well for me (I think it was suggested by my girlfriend at the time as a good brand, she had done a bunch of research about that kind of thing). I later tried several different others and they didn't seem to benefit me as much though some of them were at least somewhat beneficial.

My impression is that there isn't a very good way currently of knowing ahead of time what if any probiotics might work well for any particular person.

I’m taking L Reuteri mostly because I enjoy making yoghurt from it myself, and it tastes good. Also it’s anti H Pylori (the bacteria that causes ulcers), and I started taking it when I was worried I might be developing one

https://examine.com/supplements/lactobacillus-reuteri/

Trial and error. I've taken 6-8 different kinds and settled on one that works, which is the cheap generic store brand.

My wife has done the same, and has discovered that the one that works for her is a completely different sort.