Which, if any, fill location would require more or less force to fill
this barrel: the top hole or the bottom hole?

As you have discovered, this question is of less value
than some of the other questions, such as "will I need
to disconnect and reconnect hoses?"

Another question I would ask is "if the top hose splashes
into the barrel without a full siphon connection, would I
be in for less trouble with a small centrifugal pump?" I'd
expect having the water trying to backflow out the pump
everytime I shut it off would be more annoying than the
extra effort, or the complexity of adding checkvalves...

--Glenn Lyford