If I remember rightly the Chorus ones have ball bearings in their mechanisms for a smoother and faster action.
Also some of the cheaper ones will only select up and down by one gear, while the top end ones can sweep through the lot in a single stroke.
It's difficult to comment further without knowing what age they are etc.
The number of gears you can go up/down by is, I think, the same across the board for 9-speed. The cheapo "Escape" mechanism only allowing one-at-a-time shifts applies to lower-end 10-speed stuff although I think it's now been ditched for Veloce groups and the old shifting pattern reinstated.
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