All are nice names. Have you tried calling her one for a day, then change the next day etc, see if any stand out or you go off them?
Holler them across the park, again you might find one that fits better!
If there is more than one way to say a name, are you ok with the variation? Because someone will use it, even if you constantly correct them. Likewise with spelling. Sofia is quite Disney at the moment. Sophia, pronounced with a y sound, I prefer. But I'm not sure it's the way people would say it on first seeing it.
Imogen is lovely, I know 1. Gets called immi, if that bothers you.
Marissa, not so sure. I like it with 1 S more, pronounced mar-eee-sa. Like Marisa tomei, fab actress.
Ariana is a bit cruise ship for me too. But probably not something that I would connect to if I was introduced to a lovely baby with that name!
They are all very pretty, of all of them I think Imogen is the nicest and least likely to get messed with. Also it would suit a girly girl or a tomboy, and everything in between. The others are maybe a bit girly, but that's just my taste.
Congratulations on your baby, take your time, the right name will come to you!