Plain edge blades have one continuous edge and they can be great for cutting, chopping, shaving, and slicing.
Generally, a serrated blade is a combination of a plain edge and serrations, usually towards the back of the blade near the pivot. The benefit of serrations on a blade is that it can be used for sawing through limbs and rope.
Overall, when choosing between a blade with a plain edge and one with serrations you need to take your needs into consideration. Serrations take up space on a blade edge and are more complicated to sharpen.
That said, if you like having options on your blade edge, this sharpener from Smith’s can get those serrations factory sharp within a few minutes by the fire.
If a knife’s blade is small, like on the CIVIVI Qubit, we prefer for it to have a plain edge for more utility; (photo/Anthony Sculimbrene)