Well nen, chakra and reiryoku r very similar with the different es being how they r explained and the limitations the writer gives to the concept in support of their story.
With personaly traits mixed in to it n the types to it nen gets the 'more indepth' award, chakra is cool n was explained well but towards the end that manga became a hala baloo of madness n the very limitations constructed from the beginning were forgotten n all that mattered was the size of the tech above everything else.
Anyone with a larger quantity of reiryoku is to some degree(very large at that) stronger than u is kinda what nerfs reiryoku the most, I mean guys like Renji have been training for God knows how long but in comes Ichigo with 3days worth of "proper" training n them centuries of training guys now just look at boy wonder play whack n swing with his extra large sword for their 'salvation'.
Haki is simple n for me different from those other three to an extent, n even though after the branches of it r said n its simple, Oda still finds ways to make more from it n u just wanna see more n more of it. My fav is haki though when I fully get into HxH it shld b a close third/second as i kinda do love innocence from D gray man, there is also the energy concept from Chrome Regios but who knows what I will feel when I'm more into the story.