...but let's face facts. As a light used for self defense purposes, THEY ARE TERRIBLE.
Yes, I know that back in the day every cop walking the beat could be found to have a Mag-lite on hand at all times to use in conjunction with his Smith & Wesson model 19 revolver and that they managed to use them successfully... but the reason they used the 4 D-Cell mag lites back in "the day" was because they were pretty much the only available option. Times have changed and technology has changed with it. Today there are lights that are small enough to fit in the palm of your hand that put out good amounts of light, with almost indestructible LED lamp elements that never blow out, and that don't weigh more than a .44 magnum with an 8 inch barrel on it.
These new generation lights can be had for VERY reasonable prices and are MUCH easier to carry on your person at all times and to use in conjunction with a handgun, which is the main personal defense weapon for most people in the US.
Yes, I know you can't crack a grizzly's skull with one of these smaller lights, but I would challenge those who bring that up as a reason to keep using a Mag-lite to tell us whether or not they go about their daily life with one of those big beasts on their belt or in their back pocket at all times. The answer, dear reader, will be NO. Buying a big, hardly carried, hard to use light simply because it would make a better impact weapon is about as sensible as buying a Walker Colt revolver as your primary self defense handgun because it will make a bigger dent in somebody's skull when you pistol whip them with it.
There are dedicated tactical lights out there meant to be used in conjunction with a weapon under stressful conditions to stop a threat. YOUR MAIN CARRY LIGHT SHOULD BE ONE OF THESE LIGHTS. Leave the mag-lites (this also applies to mini-mag-lites) at home or in the trunk for less deadly emergencies. Stick to dedicated tactical lights for every-day carry. Every tool has its limits. Mag-lites are great tools for what they are... but they are NOT the best tool for every job.
Now that we've dealt with the dinosaurs of the flashlight world, which of the modern dedicated tactical lights should you choose?