Since you have Amex Everyday, I'd dump the Amex Blue. It's such an outdated card that Amex converts some of them to Everyday cards, but since you already have one Everyday card, I doubt you need another one exactly like it.

Amex is dropping their relationship with Costco next month, so I don't even if this card will exist soon. Any reason to keep that with that in mind?

Keep the Chase cards you have. Due to Chase rules about "no new cards for you if you applied for 5+ new cards from any banks in the past 24 months", you may not be able to get other Chase cards anytime soon.

There are many other Membership Rewards from Amex that you could get (especially once you clear out one or two of the least useful ones you have). Go to the American Express forum here on FlyerTalk to explore that.

If you're interested in the oneworld alliance, there are several different AA cards you can get (and in some cases repeat), most with 50k bonuses for $3k spend in 3 months. Go to the Citi forum to explore that. And some of them have no foreign transaction fees.