... what pleases you. I buy what I like and I wear what I buy, albeit I have a very small collection. All that I buy I keep so I can pass them down to my three sons. So, make sure that whatever you buy it is because YOU like it and not what I say or anyone's suggestions. 
Of course, you now added the 5170 into the plot to keep your 5980 company. LOL
Well I like the 5170, which, I believe,replaced the 5070. It has a nice in-house 29-535 caliber and is a manual wind. I like the type of pushers as I stated previously, over the 5960's round, stopwatch looking pushers. It is a little smaller (39 mm) than the 5205 (40 mm) you were looking at. BTW, got to play with the 5205 today, gray/black dial. Very nice piece.
Aesthetically speaking, I'm not a fan of the applied markers and would rather have the Roman numbers like the 5070. To me, the applied markers are too thin and too long. The sub dials are slightly off center, sitting below the halfway point and I don't mind that. What I do mind is that it cuts into the Pulsations Meter. Not sure if it could've been done but if the sub dials were a little closer together toward the center it would've opened the entire pulsations meter, making it, IMHO, a cleaner looking dial.
I do have a question of curiosity, though. The 5205 is not a chrono, has a 24 H subdial, day/night indicator and an annual calendar feature. Are you creating a theme of chronographs since your two choices are chronos or is it you just happen to love these two models?
All in all, I'll end with how I started...buy what you like. 
Aloha, my friend,
Bob