I have 12 X 50's for spotting waterfowl and scouting (truck bino's), but when I hunt I carry 8 x 42's.

Why? Because the 12's give me great long range viewing, but as said viewing area is smaller, also due to the higher magnification shaking is pronounced when free handing these nocs. Lighter and more compact is probably the biggest reason I tote the 8's. Finally picking up your object is much quicker with a set of 8's (larger viewing area).

If your constantly scanning long range 300 plus and you want to field judge, then really the bigger the better provided you have a rest or tripod. (ie spotting scope)