Freightliner makes low end and high end chassis and everything in between, so it's hard to compare generic "Freightliner" to the Spartans, which are all toward the higher end of the scale. I suspect that Newmar did not use any of the cheaper Freightliner configurations, though.
Location might be one factor. If you travel on the East Coast, the excellent Freightliner Factory Service in Gafney, SC is available to you. If you are more likely to be in Michigan, then Spartan is a good choice.
I believe that FL has many more service centers than Spartan, but many of them are oriented strongly towards truck service and may not be all that responsive to RV customers. Even the ones designated as "Oasis" RV service sites. Spartan service outlets tend to be associated with the RV industry in some way or another. You can Find Spartan Service Center
here. For Freightliner, look at Freightliner Service
. Cummins service centers will do both brands.