I am not sure the bank would protect you if the funding is not coded as a purchase, but a Cash Advance.

Western Union disclose this on its own website about sending money online using CC. Of course if you use a debit card, there is no cash advance to speak of.

I seriously doubt one can send money using CC and the funding would be coded as purchase instead of cash advance.

Instead of trying to decide which CC to use, OP should spend time to find out if the CC funding is treated a Cash Advance or a purchase.

Common sense tells me this would be a Cash Advance. Though there might be exception but since this is Money that we are talking about - since when one can buy Money with a CC after the Mint died? (exclude the AMEX GCs and Visa GCs at drug stores, the real, readily available Money that we are talking here.)

Besides, if this works as purchase with a small service fee, I am sure tons of people here would have been sending money via Western Union so to meet their spend requirements on new cards, as well as racking up miles and points... I am afraid there is no such free lunch.