Guard bar/ring should be self-explained in the difference.
Most of the time, guard is drawn as "ring" type, but sometimes, the "ring" is soft-tied and so cannot be fully classified as "ring" and most of the time, to save space, there is no "ring" and just a "bar" to block between blocks
The bar should be a line while the ring usually is a close loop. Usually the ring will be better for noise isolation because it blocks noise in all directions.
if your block or devices must be protected on all sides, it's better to use guard ring. that's ideal but if area is an issue, you may not make it a ring.