If I bought a splitter, vertical is the way I'd go. What is the downside?
The horizontal/vertical splitters are probably the cheapest on the market and they are pretty darn good. My dad has had one for over 15 years and we have split a ton of wood on it. I would guess 100+ cords have been split with that 25 ton Yard Machine by MTD and all of it has been split in the vertical position. The down side to a vertical splitter is that you cannot use a log lift on it and a log lift would be really, really nice on the 500 pound rounds because trying to get them onto a vertical splitter plate can be painful. The other downside to working with a vertical splitter is having to kneel down all day, or sit on a milk crate all day. I NEVER would have even dreamed of a horizontal splitter until I started thinking about buying a new splitter and some people on here gave me links to some high end splitters wherein I saw horizontals with a log lift.
And our 20 ton MTD with 5 hp B&S engine has split well over 200 cord and is over 20 years old. And I'd bet there have not been more than 4 logs split horizontally on this machine.
Downside is you can't use a log lift? To me that is an upside! It is no more difficult getting a log onto a vertical splitter than onto a log lift! In addition, I believe most log lifts sell for $800 or more. So why spend $800 if it is not needed. As for getting those big rounds onto the splitter, that is where you use cant hooks. If you are cutting logs that heavy for sure you need a cant hook after you cut the log so it is not any additional expense. A cant hook can be man's best friend at times.
As for sitting on a milk crate all day; definitely if you don't sit right it can be uncomfortable. The way I do it, there is no discomfort and the best benefit is that I can use leverage to help turn the logs. If it is not the right height that you want, raise or lower it! That is simple enough. I tried sitting higher but it definitely did not work as well. But if all you want is to stand while splitting and have a cool tool, then get the log lift. It is your dollars.
One more comment regarding Verticle vs Horizontal splitters;
If you often have a lot of un-even / angled cut rounds, they can be difficult to get in and should in a Verticle splitter. Whereas a Horizontal splitter you just drop it on, and it has nowhere to go. Almost ALL my rounds are un-even and or angle cuts. I don't know how I could ever split with a Verticle.
There is absolutely no problem splitting a round that is cut on an angle. It is simple and easy on a vertical splitter. I split a goodly number of logs every year and have never had a problem doing it.