The Iron & Oak in my signature has been blasting through rounds for 3 seasons now. I, and everyone who splits with me, LOVE it. I have used/rented bigger and better but can't justify $6000 machines, no matter how much I want to. :coolgrin:
Horizontal machines with log lifts and tables to catch the splits are probably the most productive if you split big rounds fairly often. I use the vertical mode on my H/V to halve or quarter rounds into manageable sizes before going horizontal to resume production. Log tables/cradles and log dis-lodgers are fantastic if not must-have features to add-on if the machine doesn't already have them.
Ton ratings are to be taken with a grain of salt. I have seen 16 ton machines split the monster rounds and seen 27 ton machines struggle with a 15" knotty bough.
Cycle Time (Cylinder Size vs. Pump GPM) should be the #1 consideration as to the productivity of the machine. Some here will disagree saying you don't have to use the full cycle, can't outwork the machine anyway, etc. All true. The way I see it, with the splitter running, I'm not there to multi-task, I'm in it to make big rounds into small splits. I don't stack while I split. I usually split and toss the splits into a pile to stack later or a vehicle to haul home. If the wedge on the machine isn't moving, I'm wasting time and fuel. Don't fret over a 1 second difference but there is a huge difference between running a 18+ second machine as opposed to a 12 second unit.
Machine construction is often overlooked (especially at lower price points) but there have been problems reported with units that have the cylinder mounted mid-casing as opposed to a heavy clevis on the end. If the cylinder hangs off the end of the beam, these are the machines I'm talking about. There have been weld/casing failures causing hydraulic leaks. You do not want to swim in hot hydro oil.
Larger hydraulic reservoir usually mean lower fluid temps and longer hydraulic component life as a result.
2-Stage pumps are almost universal now unless you find a older used machine or a home-built unit. They actually are 2 pumps in one with the second pump having it's pressure relief set lower than the primary stage. When enough resistance is met, the pressure rises and that pressure relief opens, effectively disabling that half of the pump. The other stage continues to the higher pressures required to split the log but the total flow from the pump is usually halved, slowing cylinder travel and reducing power requirements from the engine. This allows smaller, more affordable engines to be used for a given ton rating while maintaining fast cycle times for small logs and the return stroke.
Engines: I personally do not care for the units that use a vertical shaft "lawn mower" type engine as they are usually noisier and tend to be less reliable than other choices. On the upside they are relatively inexpensive to replace and you may not have any alternative depending on your price range. Any engine that you take care of will last for many years on a log splitter. I will offer a professional opinion tho. I am a fan of Robin/Subaru small engines. They start easy, run quiet and are rock-solid reliable. They typically are much less $$ than a Honda GX series engine as well. I have nothing against the Hondas other than the price tag as they are a great engine as well. Briggs & Stratton is probably the most common engine out there and they do make some good engines too. But they have many levels of quality and often the difference are near impossible to see by the exterior of the engine. They have a base level, the Intek, Intek I/C, and the Vanguard line represents their best efforts. Here's a hint that applies to ANY small engine. Look for the EPA emissions tag attached to every new engine. Does it say the engine is rated for Moderate, Intermediate, or Extended use? That's a very good clue as to what your buying and how long that engine was designed to last. Pay no mind to any actual hour rating (ie. 100hrs) that may be listed as the engine's useful lifespan will far exceed that number. Only the Moderate, Intermediate, or Extended rating is important.
It doesn't look like you want to split crazy huge rounds so I'd say the 20-22 ton machines offered by various manufacturers would suffice quite nicely. Remember even if your not splitting long pieces you don't have to retract the wedge all the way so you can shorten the cycle that way.
Some links to the different machines available that many here own:
http://www.timberwolfcorp.com/log_splitters/
http://www.ironandoak.com/itemlist.php?mode=category&categoryid=103&parentid=0
http://www.braveproducts.com/itemlist.php?mode=category&categoryid=103
http://www.northerntool.com/shop/tools/category_logging+log-splitters
http://www.tractorsupply.com/outdoor-power-equipment/log-splitters
http://www.troybilt.com/webapp/wcs/stores/servlet/category2_10001_14102_55971_54998_54998_-1
I'm thinking this thread belongs over in "The Gear".