Both unclog pores but in different ways.

Salicylic acid works to unclog pores by breaking down fat/lipids/oils. Since most clogged pores are majorly composed of sebum (your skin's natural oil), it'll break that down pretty well. Once that happens, the other components (dead skin cells and dirt) will be easier to wash out. But the problem is if your clogged pores are deeper in and have a larger number of dead skin cells/debris on top of it. You can imagine why salicylic acid will have a more difficult time breaking down the oil because not a lot of it will reach the area and instead be washed off.

This is where clays come in. As a bunch of the other comments here say, clays do well to draw out both oil and moisture towards the surface of the skin. You will get the strongest pull with bentonite. Clays will not only draw the slightly deeper impurities but also the ones that are REALLY deep inside (like ones you didn't even know you had). This is one of the reason why people "break out" after a week~month of using clay masks for the first time, because all the deeply buried impurities are drawn to the surface. (The other reason is the acclimation period from your skin trying to adjust to a new environment aka the clay/product) Once the impurities are drawn to the surface, clays breakdown clogged pores through exfoliation which you can say is a physical process while salicylic acid breaks it down by a chemical process.

Plus, clays like bentonite likes to hold a negative charge when combined with water. This is a nice bonus since it helps extract heavy metal toxins (usually positively charged) that may have built up throughout your day of walking around in a city or whatnot. And clays are also natural for those that look for natural routes of skin care.

If you are going for superficial or surface level unclogging/cleansing, I think salicylic acid does a great job. If you want to tackle the deeper impurites, I think clays are the way to go. Just make sure to follow up with a moisturizer (even if your skin is oily). It's great to use both as well to target the full spectrum in my opinion.

Hope this helps!