Yogurt and pickles.

Kefir!

Kimchi. My favorite is from Chi Kitchen in Pawtucket RI.

Because having higher biodiversity in your gut microbiome is associated with various health benefits, including reduced tendency to acquired new allergies, it seems that the more probiotic strains present, the better. Therefore, a supplement offering "5 Billion Probiotics!" with only one or a few strains may be less beneficial than than one offering 40 different strains.

Probiotics supplements that are always kept refrigerated at a suitable temperature range are said to have a tendency for greater potency, simply because more of the cells survive.

I would just cycle through whatever you'd like to eat and include at least one probiotic source. For me that's usually yogurts(they're a good snack after a walk and it's easy to sample different ones).

I tried so many of them, I use now Raw (Garden of Life) refrigerated probiotics, they seem to work in my case.

My educated guess based on science I've read:

A combination of a probiotic juice containing postbiotic metabolites(they're what maintains a healthy microbiome) with a high dose(billions of CFU) freeze dried one might be optimal. I strongly suspect that taking them with each meal to give them a competitive advantage in colonizing food during transit and subsequently deposition onto colon walls is beneficial.

Response to individual strains is highly dependent on your existing microbiome, so just try whatever contains a decent variety of at least lactobacillus and bifidobacter strains. I've had luck with JoyDay probiotic juice concentrate plus Swanson's Ultimate 16 strain one.

Probiotics are often unnecessary. A healthy microbiome can be fostered by eating plenty of fresh fruits, vegetables, and fermented foods (yogurt, kefir, etc). There's lots of beneficial bacteria in the environment on the outside of fruit and vegetable for example. High fiber diets also make the environment in your gut better for these microbes so they're more likely to stick around.

I think that probiotics are great but are no replacement for a balanced diet with plenty of fresh fruits and vegetables.

I tried a lot of different ones (over a decade). pendulum and seed both worked the best for me and ended up with seed due to cost.