Which is more reliable. For example, in setting steel posts in the ground, the pole should go under ground 1/3 of its height from the surface up. In IBC, steel post depth is made rather on a storey foundation, calling for 18" depth for 1 storey/floor, and 24" depth for 2 storey/floors. Which should be followed?
You don't get to pick what code or standard to use for a project, the local governing authority has established a code and all applicants for a building permit have to follow it, even state when it has to construct roads and bridges, or other public projects has to follow these codes.
Also the examples you used don't sound correct. In the case of steel columns, there are specified load combination factors(such as LFRD) and design criteria, building types, fire protection, the utility of the column as axial or lateral load bearing member, etc. But in all the cases the columns are supported by a concrete foundation through a base plate and anchor bolts all designed according to governing codes.
For example, the state of California has its building code. The city of Los Angeles has adopted this code with some modifications.
Building industry institutes, such as AISC, American Steel Institute, or ACI work closely with current codes and upgrade to comply with the latest codes.