For me, a handgun is offensive if designed specifically to be used in scenarios where the target can retaliate with equal deadly force, (as there is no offense without defense!
) or something that must substitute for a rifle when the latter is not practical...
And if it has most /all of the following characteristics suited to give advantage:
1. Suppressed - so that attention is not immediately drawn to your position, increasing your chance to neautralize as many of your opponents as possible.
2. High capacity - a mag change should be the least in mind when picking off multiple targets, and double tapping a standard option.
3. Armor piercing - less likely for armored/shielded targets (car doors, kevlar) to turn the tables on the offense, or be able to flee the skirmish area and call for help.
4. Medium range accuracy and potency, up to 50 yds IMO
Generous size is not an issue, but reliability/durability is a must. Other considerations would be the light weight, a fast trigger for better rate of discharge, all-weather design, glove-friendly, nightsights, and laser/flashlight devices an option.
The SOCOM, Tactical and Five-seveN come to mind.
For defense, something that could easily be drawn to action in response to a very close threat, able to fire quickly, and where capacity is not the most important issue.
Just my 2 cents