The slickest cream I have ever used is Cremo Cream.
Although Cremo gives good shaves, I don't keep it in my rotation.
I just do not like at all the way this cream smells.
Among the shaving creams I regularly use, I would say that the slickest are Proraso, T&H Ultimate Comfort, Castle Forbes Lavender Oil and Trumpers Coconut Oil.
That's my opinion.
but I have limited cream experience:
Art of Shaving Unscented
Art of Shaving Sandalwood
Anthony Logistics Shave Cream
Jean Paul Gaultier le Male Shave Cream
I haven't tried half of the soaps described above, but Real Shaving Company is by far the slickest stuff I've used. I had to do a 2 minute shave once (late for work!) and hand lathered with it. The longest component of that shave, no jest, was getting slick shaving cream off my hand. Just had to keep washing with regular soap. I was afraid to hold my SuperSpeed my hand was so slick!