I particularly like your suggestions of
Margaret and
Margot.
I'm not a huge fan of
Sylvia; I think the 'lv' combination reminds me of names like
Elvira. I do like it rather better when spelled "
Silvia" - that spelling looks lighter somehow.
On the positive side,
Sylvia makes me think of the forest (sylvan), elves (probably because of the "lv" sound), sprites (sylph) and silver.