All this is just my own opinion.Buckshot is deadly at close range because of multiple hits. You won't get enough velosity from any shotgun to cause damage from hydrostatic shock, or get any kind of meaningful expansion. Multiple hits and complete penetration are what you want. Harder shot will pattern better and penetrate better. Larger shot penetrates better, I will only use 00 0r larger. Range is critical, if your hunting deer sized game you need to keep every pellet in an 18" circle . Whatever range you can do that at is your maximum range. You may have to limit yourself to ten or fifteen yard shots. With that sa[d you may think "Why bother using shot guns and buckshot?". Well a lot of the places I hunt have a maximum visibility of fifteen to twenty yards and often the shots you get will have to be quick ones and a fast handling quick pointing shotgun is as good a choice in that situation as it would be hunting birds in heavy cover.
Like I said, that's just my opinion, but I formed that opinion over 40 years averaging around 3 deer per year accounting for literally several pickup loads of whitetails.