From my experience difference sc/difference service level. Let it be local car/import car. Try to stick with the sc you are comfortable with(good service/spareparts availability etc). Even some small service dealers can provide good service. But for major issue issue i recommend you send your car straight to a bigger sc.

In your case for proton sc, some sc will even take your car even with walk in customer but of course u have to wait. U'll be surprised some other make sc's need to book at least 2/3 weeks in advance to get their car serviced.