Interesting having four people going in on the purchase.
I would break it down a little further than hydraulic vs kinetic.
There are several styles in the hydraulic splitter category, typically based on wedge style, but not entirely.
Horizontal/vertical, which are wedge on cylinder rod.
Horizontal, wedge on beam. (options: tow from different ends, often higher beams, log lifts, four/six way wedges, disappearing four-way wedges that drop below the beam)
Horizontal, wedge on ram. (dual split, log lifts)
Horizontal, box wedge. (Tempest is a brand comes to mind, dual action)
Raised Vertical. (PowerSplit style with wedge on ram;options as four-way wedge, log lift, self propelled models, and integrated conveyor)
The kinetics are pretty much one style, the difference being up to now, two things: dependability, and single vs two handed activation.
Without exception, the kinetic splitters have narrow cutting wedges. (Hydraulic wedge design is all over the place. Dual split wedges being knife like. Timberwolf is the opposite, with an extremely fat wedge. There are combination wedges that are narrow with a wide flare to cut and pop splits.)
There are some option differences among kinetics.
Towing, lower center of gravity, manual log lifts, brand of power units, including electric powered.
I would pay less attention to tonnage claims, and more attention to what your splitting dictates (size of rounds) and how you work. An example would be taking the splitter to the wood, or the wood to the splitter, then ergonomics as in a tip-up horizontal/vertical, log lift, or neither and noodle the few rounds that may need it. The kinetics are very ergonomic with the added height and especially the table for re-splitting, but not all of them tow well. Towing may be a factor for you with four owners. I suspect most kinetics would need to be trailered for road travel.
If the kinetic is still on your list, call Paul at SuperSplit and ask if he can give you a name of someone close to you that has one that you can contact via email or perhaps personally, to check see if it is still a fit or not. I did that several years ago before buying, contacting an owner by phone. You are welcome to try mine, a three year old SS-HD, but it is probably a three hour drive for you one way. I suspect many, like myself, who have moved to kinetics, previously used hydraulic splitter and kept them. I upgraded to a hydraulic with log lift, but the really large dia. wood supply is no longer available, and the unit sits mostly unused as I prefer to use the SS for most wood.
I'm sure others can add more to the style and differences in both types.
Just read the last two posts that came up, so double coverage on some stuff. Kevin in Ohio did a wonderful job of pulling several styles together in to a beautiful custom splitter build tailored to his wood supply and how he works.