I guessed that
Tova would sound like toe + va, TOHva; this site confirms that. And it puts me right off. No doubt it'd work just fine in
Israel, but in an English-speaking environment ... I'm fond of toes, but they aren't the most popular body part for some reason.
I like
Greta very much, provided it's got a short e, as if it were
Gretta. And I think of it as an independent name, not a nn for
Margaret (which I also love and would use rather than
Greta, since it's a family name).