I couldn't find any pictures of the CIS's main capital ship like Grievous had, so I had to settle for, yes, the Banking Clan frigate. You could maybe do a Techno-Union ship or a Droid Control Ship. If the frigate was fully automated, there'd be no need for a bridge, would there?
You could also do a Venerator-class star cruiser or an Assualt-class frigate for the Republic.