Post frame and pole barn imply for me that the lateral bracing is a result of embedded posts or poles. On top of a foundation requires lateral bracing being added. Yes it can be done but you loose some of the advantage of embedded poles.
this is what everyone gets wrong. its not just a difference in name, there is a functional difference too. The difference between the two structures are in how they are laterally stabilized for wind (as well as earthquakes and anything that could impart a horizontal load).
A 'pole barn' uses the vertical posts embedded into the ground functioning as cantilevers - the post is restrained from rotating at its base through the ground embedment. This is a very simple system (which is a benefit) with the problem of post bases eventually rotting from the ground/water contact, loosing your rotational restraint, and the structure then leans sideways eventually falling down (downside to the simplicity).
A 'post frame" has vertical posts that are "hinged" at their base connection with (usually) some type of concrete foundation. There is no restraint to rotation at the post bases. Rather, the post frame uses its above grade structure through member arrangement, sizing and connections between members (ie creating a "frame") to laterally stabilize the building. This is largely how steel and concrete buildings are structrually designed and constructed as well.
It is hard for a lot of engineers to understand lateral structural systems in buildings so I get that the non-engineer crowd mixes this up too but there is a reason for the difference in nomenclature.
For the OP, if you have to build up your base with fill, it will be very hard to create the embedment needed to satisfy the rotational restraint required of a pole barn. Post frame is the most logical choice.