Pineapple!...but the really ripe ones take on a "wine-E" smell, like a pineapple wine, sort of...
And those with the "Wine-E" smell should be used the same day...they can go bad fast.
I was looking for some descriptive terms...mostly they say a "Tropical" or sweet smell....I'd just say that the ones that have the most pineapple odor are the ripest.
I do see a caution not to buy all green ones, they must have some gold-color to them, and it starts at the base, more gold, riper friut. And at the base (But on the side)....it should give slightly.