I've seen people die quick and slow unfortunately.. some examples:
Fast - i.e. getting hit by a speeding truck hit & run, skull smashed to pieces and brain spread across the road (thus terminating mental capacity instantly). The guy didn't even see the truck or register the hit.
Slow - i.e. cancer, talking and walking one day, as the days go on they get worse and sent home. Seeing them day on day massive pain, burning up, yellow/green as their bodily functions going nuts and starting to decompose, lapsing in and out of consciousness and finally breathing laboured and passing away.
Between the two - fast where you are unaware, however is more instant shock to people, vs the knowing that someone is going to die for people that know me and knowing inch by inch "just get it over with" would be the thought on my mind..
I would prefer fast but at the same time I wouldn't wish either on people I know but a long process gives them time to adjust (but doesn't ease the pain).
I'm aware that my consciousness started from nothing and will become nothing. The only product of it's existence is it's impact on the world.
My body is built from star matter that just so happens to sat on the planet, when I die that matter goes back to the planet and eventually when the sun destroys the earth (after being recycled many times through many people - including my own life) will eventually become star matter once again.