Splash lubed compressors have a “dipper” at the bottom of the piston connecting rod. So as the crankshaft rotates, the dipper plunges into the oil pool splashing it all over the inside of the crank case. This does an excellent job, but it does not reach important parts of the pump.
Pressure lubricated pumps have a crankshaft driven oil pump to get the oil where it’s needed most. The pressurized oil is directed through passages inside the crankshaft to lubricate the crank & wrist pin ends of the connecting rod. This is especially important for the wrist pin which attaches the connecting rod to the piston where the high heat of compression is generated. And they have a replaceable oil filter to trap dirt & contaminants between oil changes.
When maximum durability & reliability is desired – choose a pressure lubricated compressor.