I am by no means an expert (as many of the other denizens of this forum will wholeheartedly agree). But I do like to rattle the cage a bit...
I've only been running a stove 10 hours a day for a little over a month now. I've been picking up as many different bags of pellets as I can find, on the advice of this forum. I may be at a bit of a disadvantage with owning a Harman, most say they will burn most anything reliably. I've also burned no more than three bags of any one brand before going on to another. Not a great test environment.
The best heat I've gotten from a brand was Orford 100% softwood, picked up recently at a $4 a bag sale in Uxbridge MA (1/2 ton purchased, due to the price). They burn hot, but they seem to burn faster than any of the hardwood and or hardwood/softwood blends. Not too bad on the formation of clinkers either, compared to the others. This may be due to me running the stove hotter / longer due to a 5 hour power outage, temps in the house dropped a bit.
Just poured in a bag of Maine's Choice 100% Hardwood, Walmart purchased yesterday @ $5 bag. Cranked the stove up a bit more than the previous run with them, giving a nice clean flame, but a dirty blackish gritty ash (Orfords was a softer fluffier brownish ash).
I've not paid more than $5.49 per bag for any of what I've been burning. Looking to find the most economical way.
There is better advice out there, out here. They'll chime in soon enough.