Madonna's back-catalogue is so diverse and expansive. My taste changes all the time but I think it's widely agreed that Like A Prayer and Ray Of Light are her best.
Erotica and Bedtime Stories both took me forever to get into (understandably so) but they're now two of my faves, especially Bedtime Stories (her most underrated and overlooked album).
All her records are great in many ways (some more so than others) but some have their flaws, like Hard Candy, Like A Virgin, MDNA and True Blue. It really depends on the mood you're in tbh.
Watching live performances of certain songs makes the experience a lot more enjoyable too, like American Life @ the Reinvention Tour and Ray Of Light on Oprah, etc, etc... She has tonnes of amazing performances a non/casual fan should get into to appreciate her work more.
Hail the QUEEN