Congratulations, great stove ! I own the P61a, next one down from yours and it works great.
Pretty much these P series Harmon's burn about any pellet but my preferred brands are listed in my signature. I too do like the Energex Hardwood for a mid road pellet. Good heat output, a bit ashy but liveable with excellent BTU per lb experience with them. Top picks, going up the ladder, those Energex Hardwood, La Crete and at the top Okanagan Douglas Fir, affectionately dubbed DF around here. But many many brands will heat your house. I have not burned any pellet that would not heat the whole house in the P61 but have run into some where you need to empty the ash pan every week
Those pellets to me are junk, other people love them, go figure.. There certainly are some hotter pellets than others, Okanagan DF would be at the top of the list for me in that regard and very low ash ( empty the ash pan every three weeks to a month), they just are expensive around these parts. But DF's are my gauge by which I rate other pellets from. Again, they all heat the house.
Also, pellets by brand can be regional.