This is more along the lines of a matter of style.
HARDWOOD
These pellets are typically firmer and have fly ash. They are typically at a lower price point due to popularity of hardwoods in manufacturing leading to an abundance of dust. These pellets are easiest to find in Michigan and locally sourced pellets are of high quality due to our low mineral content in Michigan soil.
SOFTWOOD
These pellets typically have half the ash content of hardwood pellets and contain no fly ash. That means less cleaning of your stove. They also burn hotter with more BTUs per pound than hardwood pellets when combusted at pellet stove temperatures. While less clean up is a big plus, their cost is usually a bit higher and the availability of a quality softwood pellet in Michigan is more sparse. The reason is that most softwoods native to Michigan make terrible pellets.