It depends if you’re Hispanic [name]Petra[/name], if not [name]Greta[/name].
That’s interesting, thetxbelle. I’m in [name]Texas[/name] too, and I’ve never met a Hispanic [name]Petra[/name]. It feels very “fair-skinned European” to me.
To the OP, I love both, but I’d opt for [name]Greta[/name]. The possibility of “[name]Pet[/name]” as a nickname makes me shy away from [name]Petra[/name] as a fn.
I like both. [name]Greta[/name] is more Germanic of course but it’s pretty.
[name]Petra[/name] is more my taste though. You could do [name]Petrova[/name] or [name]Petronella[/name], if you want a longer version.
Maybe it’s because I live in a city that is predominantly Hispanic but I’ve never met a white [name]Petra[/name] and the prn I know wouldn’t be easy because the R is rolled (at least it’s difficult for me). I worked with one who was from Mexico so even though I know the name is not necessarily Hispanic, I guess it just seems weird to me on anyone else. I think [name]Greta[/name] works for anyone 
BTW I believe the name is actually Greek and “fair skinned” European.
I greatly prefer [name]Greta[/name]- it has a certain oomf quality that [name]Petra[/name] lacks. Plus, I don’t like any of [name]Petra[/name]'s long forms ([name]Petronella[/name], [name]Petrova[/name], ect.) and I love [name]Margarete[/name]/Margatrethe/[name]Margot[/name] (all of which could be long versions of [name]Greta[/name].)
[name]Hope[/name] that helps!
- [name]Athena[/name]