I love talking log splitters, since I've spent so many damn hours standing over one or another, the last 15 years. Whether you're buying or building, speed is everything. I will never understand these guys who buy these stupid-slow 35 ton splitters, with cycle times long enough to take a smoke break between splits, when you'd have to hunt long and hard to find any stackable round that won't succumb to less than 20 tons.
The best store-bought splitter on earth, IMO, is a 35 ton unit that's been user-downgraded to a 4" (20-ton) cylinder. You get the big pump (18-22 gpm), and the larger motor required to drive it, and all the up-sized lines and reservoir with the 35-ton units. But by downgrading it to a 4" cylinder, you can halve your cycle times, and have something that's actually usable by someone as impatient as me.