The way I saw it Natah is who she was born as, and was who she was at the start of the old war. Lotus is the shared dream of the tenno for her, dream not of what you are but of what you want to be and all that. Margulis I always viewed as being the falsest of the identities. IMO she was never truly Margulis, Margulis was just the base chosen for her recreation by the tenno.
I ended up picking Lotus, because I dont think going back to the Natah she once was would be true to who she is now, and I don't thino she was ever really Margulis to begin with. Lotus is her present to me, it represents who she has become more than who she was before.
It gives me a little burst of glee every time I ci" or ct in a clever way. If I ever spend the time to learn registers I'll be unstoppable