These combination pliers have three different modes of operation. The front part is flat with serrated surfaces either side. In high-quality items these serrations interlock when the jaws are shut. Further back from the tip the jaws open out into an elliptical opening designed for gripping round items, this is the part most useful for tackling seized fasteners. Finally, most pliers have a wire cutter just ahead of the pivot point.
Grip damaged heads.
Grip at an awkward angle.
Grip a sheared shaft.
Look for thick comfortable handles.
Unbranded items may have weak serrations.
Unbranded items may have weak cutter blades.