C'ultiva Split Ring Pliers
The opposing "teeth" on the Cultiva Split Ring Pliers make it easy to open a split ring and hold it securely. Cheap split ring pliers have a tooth on only one side, which is much less effective. Also, the jaws on the Cultiva Split Ring pliers are rounded, which gives you much more room to maneuver the hook eye into the gap between the two parts of the split ring.
Cultiva Split Ring Pliers do cost more than the cheap ones, but from the standpoint of saving time and preventing frustration, they are definitely worth it.