I almost always compare all 3 forecasts for every swell. The swell forecasts are usually - but not always - pretty similar, but MSW absolutely blows at translating that swell to wave height at local breaks. An example would be a 7ft @ 6s SSW swell translating to a forecasted wave height of 5-6 feet in DE.
I suspect SI and SL largely generate their forecasts with data provided by NOAA, while MSW might be pulling it from ECMWF. You'd think that would make it more accurate, but again, I think it's just the total lack of local knowledge that makes their forecasts here fall apart. I also think SL, being based on the west coast, doesn't do very well forecasting the shorter period wind swell we get here.