My own opinion . . . after having gone through this decision making process myself a few years back . . . just about any hydraulic splitter will make you happy and is better than doing it with a maul or other hand tool. If you treat the splitter with care it should last you for many years regardless of what make and model you get providing you don't buy some off brand model.
Tractor Supply's Huskee and its sister clone the Speeco have a lot of fans here . . . 22 tons seems to be just about right for most anything you can throw at it and the price is right.
Arien, MTD, Cub Cadet, etc. seem to all be owned by MTD. Again, 22 tons seems to be the sweet spot for capability and price.
Timberwolfs and Iron/Oak splitters are very well regarded . . . but a bit more in cost.
Like anything mechanical, splitters can and will break or have problems. I know some folks were reporting a few years back about a batch of MTDs and their clones having an issue . . . and a few months back it seemed as though there were some Huskee owners with a problem. It happens. But generally, most folks owning either of these types (not to mention the few with Timberwolfs or Iron and Oaks) seem quite happy with their splitters and report few to any problems.
Engine: Oftentimes folks seem to get hung up on the power plant. I know I was determined to get one with a Honda engine. Ended up with a Briggs engine. Honestly, it has done quite well and I cannot complain. Starts as easily as my Honda engines.
Cycle Time: Folks often get driven up about how fast the splitter can cycle. I find my splitter (27 tons) to be a bit slower, but it doesn't slow me down that much as I often only do a partial cycle while splitting and the way I work it usually is a pretty good rate.
Ability to go vertical . . . or have a log lifter: This, to me, is a must-have feature. Sure, most of the time the wood you cut or scrounge may be easily lift-able, but many folks have found that splitting wood vertical is easier on their bodies and they prefer it . . . and even if you're like me and prefer horizontal splitting it is still nice to be able to go vertical when you're dealing with that monster round versus wrestling and popping out a spinal disc or rupturing your hernia while attempting to wrestle that round three feet in the air to the splitting beam.
Fenders, log catchers, turn signals, etc: To me, most of these doo-dads and add-ons are not really all that useful or needed . . . it seems almost as if they were added to try to sell the model and make it more attractive to the buyer who thinks having turn signals on his splitter may be desirable and more useful. The exception -- a log catcher or cradle is nice to hold the larger split so it doesn't always drop to the ground.