I also like
Martha. It feels very warm and cozy to me. Very homey, which to me is a lovely thing. I think you could avoid
Marty- personally I would never call a
Martha that, because the "th" sound separates it from that crisp T sound in
Marty. But at the same time I can see how others might. Well, I hope it's avoidable, because I agree with you- it's awful!
Martha and
Susan and
Martha and
Sally are great sibsets.
Martha and
Elizabeth is nice too, just sounds more classic than the others.