In the first case, you use the payer as an entity, and in the other case the entity is the transfer itself. The question that i would consider is: "Could the transfer exists without the payer?" I think it couldnt, but the payer can exists by itself, because normally you want to store data about the client prior to the transfer.
As always, there is not a clear answer. Developing software is a logical process, but also has creative influence. Each developer has a different point of view, and all of them could solve the same problem with different focus. And I think that's the most enjoyable thing about design
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