For defensive carry a double edged knife gives you some advantages, if you know how to use it. It makes piercing easier and offers more cuts. As wells makes it easier to thwart some disarming techniques. I won't say it is the best for defensive carry because it will come down to what you know how to use along with what is legal, and many other considerations.
For utility I personally don't like them. You can't choke up on the blade easily for more control, and as was mentioned earlier the steep grind. For piercing task I find a drop point with swedge and other grinds nearly as effective for utility work. Yes there is something to be said for having a serrated and plain edge on the same knife, but I don't think the trade off is worth it, since I almost never want a serrated knife, even for rope or cardboard. Besides if I really need a serrated blade I use my leatherman.
Spinning Cyclone Of Death