Fortunately, there's an easy answer to this question: It depends.
There are lots of opinions on this subject, so it depends on whom you ask. The answer also varies depending on what a knife is asked to do -- it wouldn't make much sense to shave with a saw, of course, and you probably wouldn't buck firewood with a razor.
Let's start with a basic explanation of the difference between a plain edge and a serrated edge.
A plain blade, naturally, has a single sharpened edge. Whether it's perfectly straight or curved upward toward the tip of the blade, the cutting surface is exactly as long as the edge.
A serrated edge has a couple of physical advantages over a plain edge. First, on a blade of comparable size, a jagged or scalloped profile effectively increases the length of the cutting surface. And second, those sharpened scallops attack the material being cut from multiple angles.
Plain edges are easier to control, generally speaking, making cleaner and more accurate cuts. They're better suited to "push cuts" and smooth "draw cuts," as would be used in chopping or slicing most vegetables and fruits.
Because serrations "bite" more aggressively than a plain edge, they tend to perform better on hard, tough or fibrous materials -- rope, steak, plastic strapping or zip-ties, to name just a few.
It's also worth mentioning that plain edges are easier to maintain. Sharpening a serrated edge calls for special tools and a different technique -- it's not difficult, but it's a factor worth considering.
So what do we prefer?
In a perfect world, a very sharp plain-edge blade will do everything that we ask a knife to do. We know that this isn't a perfect world, however, and we understand that our edges aren't always as sharp as we'd like. For those times -- and depending on what you ask your knife to do -- we have no problem recommending a serrated blade.
Take a look at the tasks you encounter day-to-day, in the field or on the job, and decide which works better for you. Honestly, it might make sense to carry both, at least for a while, and experiment.