since many people who are in the market for a Nautilus have exactly this same question. For me, the answer is the 5980/1A-014 (black dial). I was never a huge fan of the 5712, only because I felt that the combination of complications did not really make sense in a "sport" watch. When I first saw the 5980/1A, I was really into the idea of a single register, dual hand chronograph because at the time I couldn't think of anyone doing this. Also, I like the idea of a manufacture flyback. Also, if you are enterprising enough, you could use the chronograph as a second time zone (PM for details on that idea). The color of the dial is completely subjective. Some prefer the more traditional Nautilus steel blue but I like the black. The price of the 5980/1A and 5980R is the only off-putting feature of the pieces. I also like the look of the 5980R, but wearing a leather strap sport watch seems kind of backwards. If you happen to switch it for the composite strap, it takes away from the elegance.
Good luck with you decision, it's not an easy one.
Paul