I think they are both practical watches; I acquired the 311 and 317 came later. As frequent traveller, I travel to different timezone, and hence the GMT, and the long power reserve really come handy. I do agree with Anthony that the dial is busy, and somehow the 30mins counter is not really practical but I think it is more for balancing the dial.
As I have few Panerais, it is just another Panerai that I would like to collect and use them when I travel.
Personally, I think the movement is nice too, and the Column Wheel is nice to watch when I am boring enough waiting at the departing gate.
Cheers!
Nien