I think the question for this thread is a good one, but the answer is hard. The best shave soap depends on more than the soap, your water, face (if you face lather), brush, how well you work the lather, etc.
I have a working rotation but this morning it all came together, a recently broken in Semogue 610 which was an OK performer until this morning, the temperature was good, I had time to work the lather properly the tub of soap was well hydrated. It was just one of those perfect moments and the result of using my tub of P.160 was a very thick and creamy yoghurt like lather which was even better than normal, so best soap I've ever tried was P.160 which should fill me with joy, but the other side of me says that this soap is no longer made and so the remaining stocks in my possession and in the wild is dwindling and so this knowledge is somewhat bittersweet.
Palmolive soap stick, wow. I think that I may have finally found the holy grail. Had the best shave ever the other day, using some Lord blades I got with with an old razor, and managed a superb 3 stage pass, perfect. Only 50 pence from Tesco/Asda in the UK. Sorry to anyone else, but if you can find some, try it??