The creators and producers of Golden Girls and Katherine Helmond had previously worked together on Soap.

After Soap was cancelled, Katherine Helmond bounced around doing episodics before getting Who's The Boss? in 1984.

Golden Girls producers tested every single actress over 50 for the four parts on the show. If Katherine Helmond DID NOT get Who's The Boss?, you can bet she would have been cast on Golden Girls because the producers and creator of the show held Katherine Helmond in high regard.

Either Rose since apparently Jessica was more like her (I've seen only one episode of Soap), or Blanche, as she obviously could have played her well (sharing some similarities with Mona).

Rose, but I base that mostly on her hilarious portrayal of Jessica Tate.

Definitely Rose or Blanche. Just not sure which one.

I’d go with Rose

Soap Katherine - Rose
Who's The Boss Kathrine - Blanche

Rose

I say Rose as well

Soap's Jessica was more like Rose, and Jessica was a great character so I think I would have preferred her to play Rose.

I've been watching Soap and every so often there's a scene that is almost the duplicate of a great Golden Girls scene. For example Mary and Jessica talking about how the face falls when you lean over so it's always better to be on your back, or how they would sit around the kitchen table (sometimes with Jessica's daughters) and eat everything in sight. I guess Mary and Jessica were the original "golden girls" only younger.