When it comes to the differences between hardwood pellets vs softwood pellets there isn’t as much of a difference with wood in pellet form as there is with firewood. Hardwood firewood is usually considered better for wood stoves since it burns longer and has more heat energy. With wood pellets this is not the case.
A hardwood log usually has more energy because most hardwood species are denser than softwoods. This means there is more solid wood in hardwood than there is in the same volume of softwood. But when the wood is made into a pellet it is compressed so the density between hardwood vs softwood pellets is about the same.
Depending on the species and other factors, softwood pellets actually have 10-20% more BTU per weight than hardwood pellets because softwoods have resins in them that have a higher heating value than wood fibre.
There are differing opinions on which burns cleaner and produces more ash. This may have to do more with the quality of the pellets than whether they are hardwood pellets or softwood pellets. This can be affected by the pellet making process as well as the amount of impurities and bark in the raw material. The pellet stove and how it is operated can influence how clean the pellets burn.
Hardwood pellets are often sold as premium pellets and costs more than softwood pellets. Because of this many people mistakenly thinking they are buying better quality pellets when they buy hardwood. Hardwood pellets cost more not because they are better, they cost more because the raw material is more expensive and hardwoods can be more expensive to process.
When deciding between hardwood pellets vs softwood pellets the quality is usually more important than whether it is hardwood or softwood. The only real way to know which you like best is to try them both and see.