A discrete title sequence is when the titles run witha separate sequence behind i.e. an animation or a sequence that will set the mood. "Se7en" and "Arlington Road" are examples of this type of openings.
"Donnie Darko" and "Dead Calm" have titles over a blank screen, followed by the narrative opening. This brings all the attention to the titles because there is nothing to distract the viewer. This might also create a sense of suspense as seen in "Donnie Darko"
A narrative opening with highly stylised editing can look very impressive and is very time-consuming in post-production (editing). "The Taking of Pelham 123" is an example of a movie with this type of editing. Additionally this movie synchronised the image to the beat so it looks a bit like a music video which makes it even more enjoyable to watch.