The way the 2 compressor work is very similar. The piston on an oil-less unit has different rings which allow it to not have constant lubrication.
To determine which one would be needed would really be determined on budget and use. If the compressor is needed in a medical type application, it would be advised to go with the oil-less unit as there cannot be any chance of oil contamination. Oil free units require less maintenance. They are good for the average home owner who plans to use it for a few hours a week.
If the compressor is going to be run daily and/or for extended periods of time, having a constantly lubricated model is the way to go.
My own personal opinion and experience has been that a constantly lubricated model, you can expect it to run for a very long time and it will almost always be a quieter running model than those without oil. I have both types and we tried to use the oil free model the same as we use the lubricated model and it's not the same at all. We usually will run the compressor for several hours at a time then about an hour cool down. The oil free model just does not hold up to that kind of use. We ended up just using it for tires and small jobs that come up. The lubricated model is what we use for all day every day work.
It all comes down to what is needed more than anything else. If it's going to be used for light duty occasional use, then the oil free model is perfect and the price is usually very reasonable. If it's going to be used heavily and frequently, I would recommend spending the extra money to get the constantly lubricated model.
Thank you for using Manage My Life!