I'd probably go with the Chase Sapphire Preferred and the AMEX Platinum. The CSP has no foreign transaction fee, great rewards (2x on travel and dining). The Platinum for Lounge access and other travel perks. It's hefty annual fees between the two of them (about $550), but for the benefits and income, I'd definitely say it's worth it.

UR points transferred to UA, of course.

What airlines do they fly most?