i'd suggest getting both citi aa cards (amex and visa) and some chase cards (sapphire preferred, ink business cards), which give UR points that can transfer to ua/*A

ua and partners have excellent connections in europe

aa doesn't have as good connections in europe/africa; you can use aa points for partner awards, but comfy partners like ba have high surcharges (i don't know about other partners like ib)

delta miles are hard to redeem for low awards. but if you think your credit capacity can take some more cards, then might as well get a delta card or two, too