1. Reliability[/B]. This comes first from reviews and reputable manufacturers. While it's hard to "shop" for reliable, it's an attribute that can really only be discovered after shooting several hundred rounds along with which defensive ammo is most reliable and accurate in your particular handgun.
2. Shootability, is also very subjective. It's not an aspect you can put in a decision matrix until after you handle and hopefully shoot the handgun. Much of this depends on highly on the individual, how the gun feels in the hand, ease of presentation alignment, trigger reach, grip size, etc. The importance of this to me is training. The more "shootable" your handgun is, the more likely you'll enjoy shooting it a lot, and in turn, spend more time training with it. This attribute leads to more frequent training, faster presentation, more accuracy, faster follow-up shots, etc. While reliability is the top attribute, shootability is a close second.
3. Concealability, or size/dimensions. This plays a bigger role for comparisons in a decision matrix as it's more quantifiable and easier to see. However, dimensions do not mean they'll fit you better (be more shootable), or guarantee reliability. I use these attributes to narrow down choices. Concealability has more to do with your holster/carry system, clothing/attire, body-type, activity/occupation, etc.
Weight plays a role, and while it's often directly proportional to size, weight has it's own concerns. These concerns can be mitigated by a proper gun belt, but much depends on activity as a heavy gun that is overly noticeable can cause discomfort and fatigue in some situations. Still, a proper holster/carry system and belt will often negate the negative affects of even the heavier/larger guns. If one is pocket carrying, this often becomes a bigger factor. Again, method of concealment plays a big role.
ROCK6