I wasn't a huge fan of imogen when my husband first said it but it has grown on me a lot. We are actually using it as a middle name. I think it is much sweeter sounding than orly and it will grow with her better.
I'm not really keen on either of them, but of the two, definitely Imogen. The only Orly I've ever heard of is a nail polish brand. Also, as a PP noted, "Orally" could become an issue sometime around 8th grade or so...
I prefer Imogen (my grandmother was Imogene), but my husband hates it. Have you thought about Orla? I met a little English girl named this and thought it was adorable.
Re: Help us choose between Orly and Imogen
OP, Imogen for the win.