I've got hard water, so have gravitated to soaps that work well in hard water. I'd buy a soap that everybody loves (MWF) and it just wouldn't work for me. I spent 3 years DE shaving and finding my hard water soaps.
When I moved to SRs, I posted this questions about soaps for DEs vs SRs.
LINK The consensus was that it didn't matter.
However, I am more in agreement of those on this thread that say it does or might. One aspect mentioned above that parallels my experience, is lather duration. It takes me 30+ min to shave as a new guy. Many of my soaps won't make it or will dry out too fast. Sure I can add water, but I'd rather not have to constantly.