I like the name Seraphine, but I do actually prefer Seraphina. Seraphine makes me think of a princess (and I'm not big on the whole girly-girl i-wish-i-was-a-princess thing) but Seraphina makes me think more of someone magical like a faery or a witch or something, which I think is more interesting.
I like both quite a bit-- Seraphina a bit more, I like elaborate. I guess it depends mostly on the combo for me. (ie my combo is HelenaEsmeSeraphina. HelenaEsmeSeraphine doesn't work as much)
I love Seraphine and Seraphina. I'm surprised that you wouldn't go for something elaborate :P That's not an insult by the way, as I myself like a lot of elaborated names :) But yes, Seraphine is gorgeous.