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I have never been offered a balance transfer on my Amex Blue, but I did receive a 0% APR offer on purchases for 6 months in December that expired this month.
I'd like to see you combine your Capital One cards; close the store cards and get either a Chase Slate (depending on 5/24) or Citi Diamond Preferred card for balance transfers.
Given your info, I would say the Blue Everyday Card mainly because it seems more versitile for spending/rewards. However, you state you don't care about rewards and spending is equal between the two so really it doesn't matter. Maybe consider you could want to cancel the Delta card due to annual fee. I am not sure if Amex lets you move limits from co-branded cards to theirs.