You forgot Molly.
I like Greta, Molly, Maggie, Meg...okay I like most if them. Not sure what I would use though.
The only ones I don't likeare Mamie, Midge, and Maisie.
I was checking BTN for diminutives and didn't see Molly, which I thought was a form. When I looked it up it said Mary.
All the Molly's I know are Margaret. Listed or not, I think it is known as such.
All of the Mollys I know are named Molly.
OP, I don't particularly like any of the nns. To me, Margot is a name, not a nickname. Id just call her Margaret.
Not saying Molly isn't a full name too, just that is a known nn.
Margot, Molly, Greta, Rita, Mae, and Daisy are all "full names," but they are also used as full names. Not everyone wants to use them as formal names, though, or always use Margaret [which is a long name].