A 5 1/2" 1095HC high carbon steel knife does all I need for it to do. If I need to dig through roots, rock, or pry or break rock or concrete, I have an assortment of steel bars, some sharpened, some not. Of the five I have, none cost over $100. Beware of these bars which are made in China or Pakistan. The steel is usually suspect and can shatter, splinter and many of them are not sufficently hardened to keep them from bending in heavy use. Proper employment of a fulcrum is important when doing heavy prying. It reduces the effort required and also the probibility of bending the steel bar. Here are the main types of bars available:
Tamper Bar: These heavy steel bars are approximately 5' to 6' long with a flattened 2' to 2-1/2' end for tamping down the soil and a pointed, chiseled end for loosening dirt or rocks. They are typically used before switching to another tool, such as a post digger. Very useful for tamping, I find the San Angelo bare generally more useful.
San Angelo Bar: A San Angelo bar is a steel digging bar, approximately 6' long, which adds leverage for clearing rocks and roots from post holes and ditches. Mine has a 1" octagonal cross-section, a rounded spike point on one end and a 2-1/2" wide tapered spade tip on the other.
Pinch Point Bar: Used for levering and demolition jobs, these 5' to 5-1/2' long steel bars add leverage to pry large objects out of the ground. Mine has a 3/4" round handle section and a 1-1/4" square lower section with a chisel point.
Pry Bar: A pry bar is a 5' to 5-1/2' long tool made of steel and is used for loosening or levering rocks or other heavy objects.
These steel bars are heavy (lightest is 8#, heaviest is 18#), so they are not generally considered man-portable over distances. But they will do the job for heavy prying and digging, augmenting the jackhammer for concrete removal, even occasionally replacing the jackhammer for smaller jobs.
The knife I use for cutting, slicing, light chopping tasks traditionally the jobs for knives.
Codger
PS- Does Busse make a 6' San Angelo bar from infi?