Alright, so here's my theory. Recall the ending credits, where they are on the boat and just leaving. They catch a slight glimpse of what appears to be Latias, and the spirits of the two Latios. They are all flying from the sea towards the city. Now if it was Latias who had just kissed Ash on the dock, then how did she get way up in the sky out across the ocean so fast? Therefore I think it was Bianca.
I support Save Our Voice Actors, a Pokemon fan group in favor of returning the voice actors in the anime dubbed by 4Kids (seasons 1-8). facebook.com/saveourvoiceactors