I lovelovelove Natsumi. It's my favourite female Japanese name. I met a girl in Japan named Natsumi who was 13 or 14; she was the sweetest girl ever.I'm not too keen on Satomi. I just don't like the sound.
I like both, but much prefer Natsumi (it's a GP of mine). There's also Misato, which can be written with the same kanji as Satomi, only in the reverse order. I like it a lot, pretty much the same as I like Natsumi.