For Code 39, Code 93, Code 128, EAN /UCC 128:
There are all variable length alphanumeric symbology.
And their "Data Capacity" - the practical upper limit, dependent on the scanner and is typically between 20 and 40 characters.
Code 128 is more efficient at encoding data than Code 39 or Code 93.
Code 128 is the best choice for most general bar code applications.
Code 39 and Code 128 are both very widely used while Code 93 is rarely used.