I won't even fiddle with rounds that large. I find it faster and more efficient to just noodle them up. The hernia helps make the decision even easier. I split vertical 100% of the time.
I have a Super Split splitter & use my tractor to help save my back. I load the bucket with the rounds and park it by the splitter. To make it easier on my back, I use the backhoe to lift all the logs up so when I cut the rounds, everything is at waist height.
Splitting is what kills me. If I am bent over that long cutting I will take a knee sometimes so that it does not have me doubled over so long.
All depends on the size of the rounds. Bigger-more vertically. Smaller-more horizontally. I usually split more vertically, but lately have found putting the loader bucket right underneath where I split I can fill the bucket by catching the splits right off the horizontal. Then just bring the loader over to the stacks. Saves work.
Monster Maul and an old car tire to hold the shivering pieces till I get another whack at 'em. My wood is across the lake and I don't feel like trying to get a splitter across by boat. Monster Maul is faster anyways.
Like many of you, I've split with a 23lb monster maul my whole life (HS teens to 61) until two years ago when I picked up an old H/V splitter. Horizontal 95% of the time. I'm 6'3" and found the splitter too low for comfort, started hurting my back right away. I solved the problem by backing my splitter up onto a set of "car ramps" used for auto repair. That raised it almost a foot higher to a nice ergonomically correct height for me.
It works very well for me The one on the left was the first one i ever bought. Had the 8cu. ft. poly tub. Didnt last but a few months once winter hit. The one on the right i picked up for free off of craigslist. Both are 6 cu. ft. steel tubs. Now just the other day.. a brand new temper popped up on craigslist, 8 cu. ft. poly tub. Had to have it. Got it for $60, never seen dirt. Big problem i had with my ast poly tub was that the bottom of it/floor cracked. the cracks just kept on traveling. I reinforced the floor on this one with a piece of 1/8" aluminum. Did the same to the previous poly tub but did it too late. That happened after it had already cracked. Going to try and take it easy on my new one.
I have a larger metal tub one I got free. Has been used to mix con rete by a previous owner. I use it a lot for wood
My big wheelbarrow I use the most has a poly tub with a huge crack. It still works for most things so I don't mind. I got it in a package deal of a bunch of useful things that I got in a barter deal. I landscaped a neighbor's house before they sold it. They were moving cross country and only taking what fit in their car and a POD. I have back up wheelbarrows with steel tubs, different sizes. Add in the pneumatic tire hand truck and I can move a lot all by my lonesome.