Poplar spits easy, but is a very soft wood. It burns hot, but burns fast too. I have a good supply of black locust from several downed trees on our property. Locust is classified as a very hard wood on the scale. About the only think harder we have domestically is pear and osage orange. Tried to split osage orange long ago with my dad's splitter - don't ever try it. The twisted grain makes it nearly impossible to split. Locust burns great - has the highest heat content of any wood in N. America. Splits great too - is why the old timers used locust for split rail fences. And, it won't rot if left unspilt on it's side until you get around to splitting it.
Electric log splitters are ok for small stuff, but they have significant limitations compared to gas. Built my log splitter nearly 40 years ago for my senior project in engineering school. Splits wood in both directions with a sliding double wedge to avoid the unproductive return cycle on most hydraulic splitters. Have 25 tons of force on the out stroke and 17 in the return stroke. It will work 4 men to death trying to keep up with it. The axle is off a B-52 APU and the main I-beam is galvanized steel from an electric sub-station (don't ask how I got those components). Still runs great after nearly 40 years.