the EX accepts hood also, not using filter threads.I thought the new one accepted the hood & old one has to use filter threads?
The 19mm EX accepts (and comes with) a hood. The 30mm Ex does not have a bayonet moun for a hood, and requires a filter thread hood if you want to use one.the EX accepts hood also, not using filter threads.
I've only used the 19 ex and 60 art, they are quite different lenses so not comparable. but DXOMark is giving slightly better scores to the newer version.
It almost never hurts to use one (only if it would shadow an on camera flash, or get in the way of using a filter for example). They are beneficial to reduce flare if there is light coming in at an angle that the hood will block. Say that the sun is about 45degrees to your side, outside of the view of your frame, but that light could still be striking the lens causing flare. The hood may block that. Hoods also help to protect the lens. If you drop the lens/camera, the hood may bend/break, keeping the lens intact (happend to me once with a compact superzoom camera. The hood got a big crack through it, but the camera still worked. Without the hood, the lens could have broken).In which situations would you use a hood?