Hi Mike,
choice depends a bit on your lifestyle / requirements:
pro Sub: the timing function of the rotatable bezel might be practical in sports, for timing meetings, cooking etc.
pro GMT II C: it offers more functions for travellers, either indicating
- hometime and date, second timezone, UTC, or
- hometime and date, UTC, solar compass (via turning the bezel to the position which is closest to indicating the astronomic time of your location, for this you need to know your longitude)
Otherwise, many points are just a matter of taste:
- the Sub looks larger due to its "emptier" bezel and wider lugs than the GMT II C
- the adjustment of the clasp is finer, but at the expense of a rather longer clasp than the GMT
- the PCL's of the GMT II C show wear rather more obviously than the brushed parts
I recommend to you to try both models in direct comparison and find out how they look and sit on your wrist (flat bottom of the GMT vs. more convex bottom of the Sub) and then decide. I went for the GMT II C a year ago and am still convinced to have made the best choice for me.
Good luck!
Jann