The cheapest, simplest, most gentle baby soap available at the time that I need to buy some. Age and hormone shifts have rendered me incredibly sensitive (itchy, painful, dried out) to such things.

I'm allergic to perfumes so any type of soap I buy is hypo-allergenic with no scent, unless it's lemon, grapefruit, cocoa butter, or something like that in my cleaning products.

I use the "what's on sale" brand of soap. Sure, I can buy a bar of organic, non-GMO, free range, locally sourced, all natural, gluten free soap with essential oils for just $15 but I prefer to save $14 to spend on anything that isn't soap.

I usually use the cheapest available and because of sales that varies. I don't buy the cheapest when it comes to dishwashing detergent because the cheap ones I've tried didn't work as well as Cascades. I do keep some Dawn liquid dish soap around because I have found it never fails to get rid of poison ivy oil. I use powdered laundry detergent that comes in a cardboard box to avoid the plastic container for liquid detergent. My personal bar soap is often a gift from a friend or neighbor. My neighbor makes soap and she always gives me some of her new batch and I have a friend that brings me some lemon scented stuff that's wonderful as a hostess gift. In my Airbnb bathroom I provide tiny hotel individual bar soap that I got on Amazon but the bathtub also has liquid soap. I hope someday soon I can buy large refills for them in a-plastic container.

The kind my mother used to wash my mouth out with.

Basic stuff, without "marketing additives".
Its job is to clean my skin of sweat, dirt and grease, without scouring it or dessicating it.
I grew up in East Africa, where we were not bombarded by crass commerciality.