A shampoo doesn't necessarily give the hair slip, although I'm sure some folks will have a contrary view on that. For me though, the shampoo is used to cleanse the scalp. I don't really shampoo the lengths as it can be so drying. My hair can feel moisturised though if I use a good moisture rich shampoo.
As for conditioners that gives the most slip, that depends on your hair texture, relaxed or natural etc and other factors. Not all conditioners work for everyone so you may need to go through some trial and error to establish what works best for you.