If you've cleared a lot of land or have a lot of treetops remaining from a timber harvest, then faster overall operation speed may be desirable. This is achieved with a fast cycle hydraulic model, an hydrualic model with a 4-way (or more) wedge, or a flywheel model. I'm ruling out large expensive firewood processing machines because I assume you don't want that.
There are a lot of MTD clones, which are essentially the same design (MTD, Troy-Bilt, Yardman, Cub Cadet, John Deere, et al.). I don't like these as much as some others in its class because the beam is lower (harder on the back), the log dislodger is not as beefy, it often has an half beam, cycle times are often longer, the wedge design is too wide (not a two stage like Huskee/Speeco), and the cylinder has been known to rip apart on late models.
The best bang-for-your-buck in the homeowner/entry level, IMO, is Huskee/SpeeCo (SpeeCo makes Huskee). They have a higher beam with a cradle built into the beam, the wedge design is better than MTD, and you get a full beam. I purchased the Huskee 35-ton a few years ago from TSC and have been very pleased. It goes through even the toughest crotches. Although not made in USA (only assembled) SpeeCo customer service is very good. The weak link in for Huskee splitters is final assembly at TSC--some stores do this better than others.
You pay more to top brands like Iron & Oak, Brave (made on the same line as I&O), Timberwolf, and American, but one of these may be what you need.
The I&O are really nice and are better balanced than Huskee/SpeeCo (easier to move by hand because of less tongue weight). They also make an 8 sec fast cycle hydraulic. What I don't like is that you have to pay for extras: log dislodger and log cradle.
If you have a bad back or want a 4-way splitter, look into a Timberwolf or American with a log lift and table. These models will have a stationary wedge on the beam instead of one on the hydraulic ram. You don't have the option to change the orientation of these to vertical for splitting large rounds, but that's why you get the log lift (or noodle large rounds in half with a chainsaw before putting them on the beam).
The flywheel models are very fast (~3 sec cycle times), but need a couple attempts at really tough rounds. Super Split, Wood Wolf, SpeeCo SpeedPro, and DR. These excel with striaghter wood. I've been looking at a Super Split to compliment my 35-ton vertical/horizontal hydraulic. If you're not sure about these, there are a lot of Super Split videos on the Internet.
On an hydraulic splitter, you want it to be faster than you can work. For me, I'm usually a one man operation and that's about a 14-15 sec cycle or faster.
You will have options for commercial engines on more expensive splitters.
