I'd say the first question is realistically what ranges are you going to be shooting and what are you going to be shooting at?
You can easily get to 1000yds with 14x magnification on deer or larger sized game. 20x is nicer on smaller stuff or if you also want to be able to judge racks etc through the scope so you don't have to also pack along a spotting scope or bino's. I always recommend going with the 50mm or larger objectives because they really do extend your shooting times during those critical moments early and late or in dim, cloudy weather.
I have Leupold Mark IV and VXII's on my STW's and they have served me even on bobcats and coyotes at that range with 20x max magnification and 50mm objectives.
If budget is a consideration look at the Vortex Viper PST
's in the 4-16x50 or 6-20x50 or the Zeiss Conquests.
If budget and size/weight are not an issue then USO or Nightforce, or IOR Tactical long range models.