8 oz jars are tough. They don't fit into the(edit- SMALL) flat rate boxes, and I don't know enough abut the regional boxes to say if that is a good option.
Usually the 8 oz jars end up weighing more than can be shipped with First Class which has a limit of 13 ounces total package weight.
If shipping multiple jars, the MFRB seem to be the best option as weight is not an issue.