Question:
Obviously a thread asking to decide between CW and CWD can't do without a plethora of GIT recommendations..
Cool Water is a very distinctive one, but I just feel it smells like shower gel. I would recommend looking at CK Eternity as well, or maybe even Paco Rabannes XS.
Cool Water Deep is somewhat more modern, an aquatic somewhat like a darker/bluer smelling Acqua di Gio, though not as blue as Polo Blue. Quite different from the original CW, and much less imaginative imho.
Can't really comment on the longevity of the two. I would get CW or more likely Eternity, even if I didn't already own ADG.

Answer:
Definetely CW Deep. A less floral, fresher take and as good lasting as the original one.

Answer:
I recommend cool water deep as well. It lasts a fairly long time on my friend. He wears it all the time and whenever we're out somewhere I can still smell it on him after 6ish hours.

Answer:
CWD is my third favorite scent of all time. It's really relaxing and definitely more modern smelling than cool water. However, it has longevity issues. Where are all these CWD fans coming from... everyone wants to come out of the closet after a few postings lol. This is not including myself, I've mentioned CWD as my third favorite in a thread I started back in october. GET THE DEEP!!!!