I believe both kisses are actually, to me, the most perfect, but they come from different psychological spaces for the characters. The first is a hint of fate, a dollop of attraction...okay several dollops of attraction *wink* and the actual kiss of itself is the foundation.
The other kiss, the soul kiss, builds on that foundation with passion, the need to absorb the other entity, who happens to be your other half, now recognized. That is why it is the soul kiss. The giving and taking of pleasure in the others total existence, there is also a haunting quality to it, in some ways re-inforced because of its potential for goodbye. Everything they are, everything they feel is poured into the touch of lips, the sharing of breath that is deepened and tasted with pleasure and poignance. Within it, is a promise on both sides. It is communion.